I really liked the comment on giving some service away before account creation. In my experience, one of the largest hurdles to user adoption is getting something useful from the site. If a user is able to see the value of the service *before* putting something into it, they are more likely to understand the offering and accepting the reward for 5 minutes worth of forms. There are so many services competing for users attention and everyone of them are fighting for their niche. You have to put something on the table to gain the initial interest to keep the user on a site long enough to make it past the click of the back button. I could not agree more with this point.
This recent story relates: http://news.ycombinator.com/comments?id=824