somehow the "Dear all" from my previous question disappeared and could not be edited back in? Does this happen all the time or was there just something weird going on in my browser?
Yes, some salutations and closings are automatically removed from new posts.
As Peter mentioned, there's no need to add a full signature since your gravatar automatically shows up in each of your post; feel free to put any additional information about you in your profile page.
Also, the SE system draws its strength from its wiki capabilities (and more): unlike usual mailing-lists, greetings and thanks can be omitted since they are not an essential piece for building a live repository of good questions and answers. This does not mean that we are not courteous, just that we are aware that CV is a different place to ask questions. And rewarding existing answers by votes and green check can also be seen as a form of thanks.