It depends on the rush

What I did with one of mine, was to advertise the site in the UK gay press for about 6 months before the site opened.

For that 6 month period when guys went to the site, it took their registration and told them "not long now, uŽll get an email when this is all done"

... meaning that ... people understood it was a new site, and when they got their "the site is now ready" emails a few months ago, all bar a few of the people logged in and instantly saw a busy site.

Which is cool. Depends if youŽv got the budget to spend 6 months advertising on something that may or may not work or not.