It seems that some folks are asking large amounts of questions. I remember seeing one fellow ask over 10 questions in an hour!
This is getting outrageous, should we introduce a limit on the maximum number of questions per time interval?
I presume this is a tongue-in-cheek self-reference, but the question is a good one.
Let's take it as a general question -- so let us imagine that we face some case where someone posts a lot of questions. I don't think that some high number of questions a day is automatically a problem in itself, as long as the usual conditions for a question to be suitable for the site are met.
So if the questions are:
clear, well-formed, answerable questions (i.e. not in the form of a thesis) that show some basic research (awareness of definitions, familiarity with basic explanations of concepts from a textbook or an on-line resource like Wikipedia, awareness of one or two related questions already on site)
also relevant/on topic, not duplicates, not too broad, not opinion based etc and generally follow the various guidelines for asking a good question not already mentioned above
then the raw number of questions is generally not of itself an issue. We'd get what -- 100 questions a day or more on site? (This is not based on checking the figures, but one can count how many pages of new questions posts appear in the last day or so readily enough - and I sometimes do that, so it's not hard to get in the ballpark)
Good questions are the lifeblood of a question-and-answer site, and good questions are actually hard to write (a reasonably good question is harder to formulate, I think, than a reasonably good answer*) -- if someone who posts a lot of questions is taking the trouble to formulate their questions well, they're contributing.
* From my own experience at least, good questions are very difficult. While I am satisfied with a good fraction of my answers, I don't know that I am really satisfied with any of my questions. As a result, when someone can write a good question, they're a treasure.
To remove any hint of the personal from this -- at least as might be seen as personally relating to you -- let me discuss another user who in the past posted a lot of questions. As might be expected, the danger with posting more than a few questions a day was that there was a tendency not to do enough research and show a lack of thinking about comments on the question (which might often lead to suitable improvements) but simply to comment back almost instantaneously, often leading to a string of new questions in comments, each itself showing a lack of research.
Such an eventuality can be very frustrating and does lead to issues: you can for example end up with one user absorbing a lot of the effort of the people who are trying to edit, clarify or otherwise make questions answerable on site, at the expense of other people with questions -- not just because of the volume of the questions, but the lack of care in formulating them.
Correspondingly, it would also be necessary to avoid, as far as possible, holding discussions in comments (which SE network policy already asks us to avoid, but which become more crucial if you want to post many questions) -- respond to comments by improving (i.e. editing) the question as far as possible, rather than generating further questions in comments, and wait long enough to understand the answers before posting any related questions$^\dagger$). Only respond in comments where you need to clarify the comment or to directly answer a question that (for some reason) could not be edited into the question in some way (this would be very rare).
$^\dagger$ Since answers may take a few days to appear, this would typically mean that a string of related questions should normally be spaced out over time. [Multiple unrelated questions could still appear on the same day, if the above considerations are followed.]
With a high volume of questions and a lot of posted comments, there's a strong risk of annoying users, so one must strive as far as possible to work "above and beyond" what would constitute an average question quality, and to make sure there's no risk of comments seeming to be trivial or thoughtless.
As a result I think it's incumbent on a user that wants to post more than a a few questions a day to put in additional effort to make the questions they do post require less-than-average effort from others to make the questions answerable (so they're not 'hogging resources'), rather than posting low-effort low-research questions and failing to address issues with the questions when they're pointed out (which are obvious risks with a high volume of posts).
So an acceptable but high question volume is possible, but quite difficult, since the level of effort required to make the questions suitable will also be high. In particular, it is doubtful someone could post more than about two questions in an hour and still be doing a reasonable job of it, unless they were already so expert that they hardly needed the answers. [I doubt I could post more than two adequate questions in a day myself.]
Conversely, a limit on questions per day would be no guarantee of additional effort; better I think to encourage users to post better questions (via the usual tools --- comments, placing questions on hold, downvotes, closure/deletion etc) than to restrict the volume -- however, if someone posts enough bad questions, downvotes and closure will eventually limit their posting rate (the system does it automatically), but it tends to be fairly unusual to encounter it if one takes even a little care to post some good questions or improve old ones.
There's a corresponding danger with people posting a lot of answers per day, of course -- they too will tend to risk being glib, poorly explained, same-ish, and not especially useful. One way for answerers to keep an eye on whether their volume is getting too high is to keep an eye on their acceptance rate (and on upvotes/downvotes -- though that sometimes tends to be a fairly noisy indicator, if you regularly get more than a tiny fraction of downvotes you're probably better to answer fewer questions with the same total effort).
I do answer a lot of questions myself -- I will probably pass 3000 answers on site in the next 24 hours (edit: I did) -- so this is an issue that I try to keep in mind as I go along -- but my acceptance rate is pretty good (close to 1400 of my answers have been accepted) and my downvote proportion is very low (0.2% of the votes I get are downvotes), so at least by those crude measures I'm probably pretty safe. We have had users in the past with very high answer rates but pretty low rates of acceptance and much higher rates of downvotes; and in those cases there would be a reason to think that more work on the individual answers (with correspondingly fewer answers posted) is called for.
there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know. -- D. Rumsfield
The problem with using Q&A sites like CrossValidated for learning new stuff is that you can only ask about known unknowns -- things you know that you don't know. Sites like this will never be a substitute to going through a handbook, attending lectures, or even participating in one of the multiple available online courses. Questions you ask and the answers you get cover the topics only partially. So asking multiple questions may lead to illusory and fragmentary knowledge if used instead of studying some topic by yourself. So I would say that there is also a risk for the person who asks the multiple questions of gaining false sense of knowledge.
Users who ask too many questions are welcome, as long as the questions are decently good. Questions are very useful contributions to a QA community.
(How good a question is is a bit subjective, just vote. If a user asks too many downvoted or closed questions, they will be banned from asking questions anyway.)