Thinking about starting a group blog?
A few months ago I was invited to join and help start a group blog with writers from the Twin Cities. Since I already had...let's see...at least three blogs, I said no. But with some arm-twisting I finally said yes. My biggest issue was that this was a romance blog, and I thought my presence there would confuse visitors. In the end I'm not sure it confused as much as diluted the focus.
What I learned from my stint in a group blog:
Group blogs are hard. Much, much harder than a solo blog.
It's hard for a group blog to have personality, because...well, it's a group.
Group blogs aren't spontaneous. This was my biggest frustration. You have your day to post. If you have something you want to chat about, something that's on your mind, it will no longer be on your mind next week. Lack of spontaneity translates to lack of energy. The more the merrier does not apply here.
Worry over dominating the blog keeps members from posting even when things are sluggish.
Nobody is in charge. While this seems the fair way to handle things, you almost need a host. Otherwise it's like going to a party where there is no host and everybody is wandering around looking for the beer, and the CD is stuck on Green Day's Time of Your Life.
Disinterested group members. A lot of people get into group blogs because they have no interest in having a blog in the first place, but they feel pressured into blogging. They feel a group blog will be the easier way to go. YOU HAVE TO ENJOY BLOGGING. If you don't enjoy it, don't do it.
If you build it, they might not come. Big names don't translate to visitors. Many of the most popular blogs are written by unpublished writers or newly contracted writers. I've seen some NYT writers start blogs with other NYT writers and the blogs bombed.
Having a group doesn't always mean more visitors. It could actually mean fewer visitors.
A group blog takes just as much time as a solo blog. Maybe more when you factor in the planning and behind-the-scenes stuff.
It's probably not a good idea to mix genres.
Make sure everybody is on the same page, especially when it comes to participation.
edit to add more ideas:
you can't be afraid to make an ass out of yourself.