[wwwizard]

Direction is a good beginning, but after a little momentum, a PHPBB forum like bienpjr's can often sprout its topics spontaneously, I've found. With ecology so scary these days, you're sure to find some interest with your topic.

I'm newer to making blogs, but have been sysop for various BBSs since the '80s when they were dial-up outside Internet and ARPANET discussions before that. Across that history I've found that groups who have something in common (same profession or school for example, or differing politics) will soon discover their own topics. That's an inherent "direction" from which topics will emerge.

Another source can be based on identity of the author, like a blog for a band, though MySpace seems to be serving that niche community well.

I'm finding as a web designer that some website owners enjoy a diary of their creations, which can serve also as a gallery in cases where an artist doing unique pieces may be motivated to discuss his or her works.

Both BBSs and blogs can serve project discussions, though not specialized for that, their familiarity can be inviting. I've sometimes put passwords on them so such discussions can be private and confidential. In such cases the blogging becomes brainstorming or collaboration.