Why is algebraic geometry so over-represented on this site? Seriously. As an undergrad my thesis was on elliptic curves and modular forms, and I've done applied industrial research that invoked toric varieties, so it's not like I'm a partisan here. But this can't be a representative cross-section of mathematical questions. How can this be fixed? (I mean the word "fixed".)
 A: Founder effect.  The people who launched the site are mostly in Greater Algebraic Geometry, and they naturally post a lot, which in turn induces people (like me) who are inclined towards these areas to visit the site a lot.  If the site becomes widely popular I'd expect to see a distribution of questions which "looks like mathematics," to paraphrase Bill Clinton.
A: We have been here before with the arXiv.  This site is (somewhat inadvertently) a massive work of social engineering.  It is a social dynamical system, and it spreads where it wants to spread.  Yes it is the founder effect, but it is more general than that.  It is going to spread unevenly in different areas for a long time.
A: To amplify Greg Muller's answer, introductory courses in algebraic geometry tend to have a lot of definitions and wave vaguely at motiviation. So students starting out in the field often want to find "native speakers" who can help them understand how everything fits together.
I'm sure that founder effect is also a big factor, as JSE suggests.
A: I think that in some fields people are more active in the internet. There seems to be some correlation between the most popular tags here and the number of blogs in the corresponding section in the mathematics/statistics blog wiki here:
http://wiki.henryfarrell.net/wiki/index.php/Mathematics/Statistics
I do not know the relative proportion of algebraic geometers to other mathematicians but it may be in some fields the internet is more useful than others and there is more activity of the people in the field. 
A: I agree that the founder effect is a significant factor, but I also have another (more crackpot-ish) theory.  I think some disciplines, like algebraic geometry, are harder to pick up in a traditional classroom setting, or out of a book.  In practice, they are more often learned like a language, through repeated exposure and watching other people do it.  Of course, to some extent this is true for most disciplines, but I think its more true for algebraic geometry than for analogously hard disciplines.  If you grant my point, then there would be an over-representation of these disciplines on the internet, because they are looking for explanations and intuition unavailable in technical contexts.  I think a similar statement is true for category theory, for instance.
