I generally answer/ask all questions un-anonymously. I feel no need to hide my identity from people online, especially on this site. Once in a great while I will answer a question anonymously if it is something like a heated religious debate or a touchy subject where I don't want to get flamed for my personal opinion.
Never. =] I've never used the anon function in all the time I've been a member. I figure if I wouldn't want to show my face [both literally and my 'identity' as a user] with my answer, I'd probably be better off not answering at all. Usually I just say 'f.uck it' and post anyway because hiding behind anon doesn't sit well with me. I understand why people do it, but it's not my thing.
Whenever I answer a sexuality question I usually go anonymous because there are some weird people on here that would be more inclined to friend/message me seeing my answers. I ask anonymously when I feel my question is too personal.
I go anonymous most of the time because when I do not go anoymous, there is always a hater who down-votes me just because it's me. And I'm not going to give him that benefit so I just go anon.