I publish under a pen name. Here are the pros and cons I've noticed thus far:
CONS:
* When meeting other authors, new people at my publishing house, etc., there's always the whole, "What do I call you?" thing. Easily enough resolved.
* Always have to choose which name to join writers groups/conferences as, and sometimes forget which choice and complicate registration, etc.
PROS:
1) Makes it easier to separate my personal e-mail, facebook, etc. from my professional ones.
2) Gives me flexibility in terms of writing in other genres eventually, if I so choose.
3) Helps with the psychological distancing that can come in very handy after your book is out there in the world -- it's a reminder that people are talking about the writing, not the writer.
4) It's fun!