I'm also using an integrated install of UBBT and Photopost. To save on bandwidth, I won't allow unregistered users to see anything but thumbnails in the photo gallery. This seems to weed out the drive-by curiousity seekers from the people who are really interested and willing to take the time to sign up. Then, when users do sign up, I automatically put them in a "Probation" group which only allows them to view photos, and to post in certain forums on the message board. They can't upload photos, or post in the "more coveted" forums, until they've written 5 posts on the message board. I explain this in the "Welcome" private message, although I don't tell them specifically how many posts they need to write before their usergroup will change. I simply say they need to "participate and contribute to the community" and then they'll be allowed all privileges. I use the "auto group change mod" to faciliate this.
This configuration has been very successful. I've got about 4300 registered users, and I would guess that at least half of them have posted enough to get themselves out of Probation. In the Welcome PM, I direct new users to a "Getting to Know You" thread, and tell them to introduce themselves -- this gives them a place to start and an easy topic to write about. They usually do this sort of tentatively, but I have a number of moderators on the board who make a point of responding positively to every new poster. That seems to help new members feel welcome, and they feel more confident about posting.
I didn't start out running my site this way. However, my members are largely teenage girls, and I found they were just using the Photo Gallery as their personal photo album and ignoring the rest of the website (it's the official website of a "celebrity"). By limiting their access to the photo gallery and to the thread where they can actually exchange posts with the celebrity, I gave them lots of incentive to become contributors to the board. It's made for a really nice, friendly community.
