I once built a Q&A site for advance technical questions. It didn't work out. It ended up having an overwhelming amount of bots instead of people using it. A while later, Stack Overflow came online and it became a success. While it was more advanced than what I had, it wasn't too different in concept from what I made.
Looking back, it was pretty obvious what Stack Overflow had that I didn't - a following. Joel & Jeff's blog attracted a ton of readers over the years and those readers turned Stack Overflow from nothing into something.
I'm not someone who has the talent to write continually write insightful blog posts nor do I have the mindset to hype things up in forums. I'm not sure what kind of options there are for someone like me to get those first few users.
How do you prime a community for your service?
While I wouldn't call ourselves really successful, our latest venture, Fork the Cookbook succeeded by having what we call "single player mode". We had initially got people to add their favourite recipes into Fork the Cookbook (and in the last 5 days or so, this has come back to bite our asses), and thus, the 'single player mode' is essentially letting the users achieve something that can be done on their own (i.e. beautiful looking recipes for their personal collection)
Now after some amount of recipes, we're only starting to actively promote the community features (like forking a recipe).
All these came from our past experience in failing to gain enough traction on community sites. See my profile for more of my failed projects (there are a lot more listed on my latest blog entry where I was feeling rather blue).