Concurring Opinions has a useful discussion about how to prevent your blog from being linked to your real-life identity. While a lot of the discussion focuses on protecting yourself from a subpoena, I imagine the goals of many bloggers are more modest - as long as their mother and/or their employer doesn't find out about their blog, they're happy.
I haven't tried very hard to hide my identity (how many Bay Area-based JD/MFAs are there, really?), and at this point I'm just trying to maintain the most primitive level of anonymity: not having this blog come up in a google search for my name. My sense is that many bloggers are happy having their identities being this sort of open secret. I confess that I've occasionally tried to live out my fantasies of being a private investigator by attempting to figure out who certain bloggers are - not with a plan of exposing them or for any other malicious purpose, but just to satisfy my private curiosity about whether it can be done. I don't have any fancy IP address-tracing skills, so my efforts have mainly consisted of putting together bits of revealed information. From this experience, the following observations:
1. Lawyers with Martindale entries are the most traceable people in the world.
2. As Solove's post points out, it's really hard to have any blogging personality without dropping a few identifying details, real or fictional.
3. As the case of A3G suggests, a little misdirection goes a long way.
In the relatively decorous world of blawgs, which is mostly where I hang out, nearly everyone seems to use their real identity. But outside legal academia, people may be a bit more uptight about the whole blogging thing. At any rate, as this recent nutty fracas illustrates, sometimes concealing who you are has the perverse effect of making some people all the more obsessed with you.