I am "Brutannica" (as far as you need to know). The name goes from an apparent misunderstanding of a character in the much-missed 18th episode of Pokemon, not from the world's most renowned encyclopaedia. Anyway, I've been using Wikipedia since the fall of 2003 and started contributing in 2004 with some controversial edits (but I thought many were good) of the first 30 or so of Michael H. Hart's 100 most influential people in history. I stopped doing that for various reasons, and now mostly check in every day and make comments on discussion pages. Lame, I know, but it's hard for me to substantially edit any articles because I'm really not much of an expert on anything! :( I tend to change interests quickly.
My overriding passion is history and global relations and cultures; I like anthropology but am somewhat turned off by its scholarly, scientific tone. I am also fascinated by popular culture and somewhat interested in "high"er culture (and loathe the distinction between the two, which, I think, tends to be arbitrary and elitist). My edits range pretty widely, since my favorite thing about Wikipedia is probably how diverse its coverage is.
As already mentioned, I rarely make substantial edits, partially because I don't have many fields of expertise and partially because I find it personally hard to justify the enormous time and effort needed to do them. I created a mere two articles (Kusaila and Dien Bien Phu (manga)) and attempted to create another (Pattenrai!) but it's been rejected. The subject I can realistically do most to contribute about is anime (I even taught a course on it in '09), and I considered using my Japanese skills to translate Featured Articles from the Japanese Wikipedia. Sadly, so far this has not gone very far.
I can say other things, but I think I'll let my userboxes do the talking. As a closing note, I'd like to say that I ADORE this site; it's easily the most dynamic, fascinating part of the Web and has a good shot at being a major transformer of society. Unfortunately, I must also concede that it has a lot of drawbacks, from the ongoing and perhaps unresolvable controversy regarding what's fit for inclusion to the hostility of entrenched editors to newcomers. Still, I hope to remain a part of it, and maybe even contribute more meaningfully someday.