A couple of things that might be relevant:

* How many people who want to do X but haven't yet would choose your site over established-X-player?

* Would you expect people using established-X-player to switch to using your site? Why or why not?

* Does X involve substantial lock-in or network effects that established-X-player can take advantage of?

I've been seeing lots of articles (recent calacanis death spiral email, for one) saying that this economic climate will not be friendly to smaller clones (don't mean to imply that your idea is a clone).