They don't annoy me at all. You can always just answer whichever questions you want to and sometimes people like to have a lot of questions to answer or read for whatever reason (boredom, feeling helpful, etc). Then again, I'm not easily annoyed at all. Some things people get angry about shock me. I'm just curious how the rest of you feel. As for the limit, I don't have a specific one in mind but I don't think it would be appropriate to, for example, post a 100(!) question survey that you sometimes find in personal LJs.
Edited to clarify: By spreading the questions out over some time, I didn't mean all in one day or a really short period, just maybe one a day or every other day, or every few days. You get the idea. I realize it is against the community rules to make too many posts in a short period of time. :)