Found a great article detailing some of the larger well known web2.0 social websites and how they started which was initially towards niche markets.
I did post a comment on the site but thought it was worth discussing further
From the outset if you target a particular market or niche it should help to define your scope and keep you in reality. Rather than trying to target everyone and never being able to actually develop and deliver anything. Aim to provide for your niche and not everyone. This should also allow you to focus on potential revenue streams aimed at your niche market instead of just trying to build something big and hoping the revenue follows.
Next get out there and get involved and interact with the user base. If your passionate and driven about what your are doing your user base will see and feel part of something. This should add loyalty and help build a community.
From here you should hopefully start to see a community build and grow organically, hopefully if you are doing things right from word of mouth and other websites talking about it.
Hopefully if you are doing things right and planned from the beginning you should now be able to start hooking into potentially revenue streams.
You should hopefully have a growing community and a website with a sense of purpose providing a valued worthwhile service to loyal users (don’t think I’m ready for Corporate life and big profits lol)
There is also some similar information over at 37signals in the ‘Getting Real‘ publication.