Darren Rowse has a post up on relational blogging that I think everyone should take a look at. I have, a few times, tried to start blogs with friends or family members, only to have it blow up in my face, and these tips and thoughts would have come in handy back then.
1. Give it Time
2. Show Flexibility
3. Gain Knowledge
If you have a blog with more than one author, let me know about your experiences, did it make it easier, or harder to maintain?