My startup, Grosper.com suffers from the same problem. We do group buying for real estate in the Middle East and the as the description suggests, we need a lot of early users so that deals go through. If deals don't go through early on, more members won't come - a vicious cycle.
This post is about asking for help to market my startup. Any comments about marketing ideas on a shoestring budget or resources such as great books by great mentors (More 37 Signals, less College Professor) would be appreciated.