Comments that are actually answers
I've noticed that there are many examples of people providing partial answers or pointers in the comments to a question instead of attempting to answer the question. I find this practice confusing and detrimental to the organization of the site. Wouldn't the community prefer to have comments that answer parts of the question posted as proper answers instead. They could then be voted up or down and their contribution would be easier to assess.
My suggestion is to emphasize this more within the community and the FAQs and to let the comments be just that: comments about a question or answer, not an attempt at answering the original question. It should be acceptable to give brief or partial answers only.
Another suggestion is to add a verification step when posting comments to the original question where the purpose of comments is made clear to the commenter.