We actually did the same thing for Kongregate. Except we gave out an invite code to everyone who asked - usually same day. So the artificial scarcity was... art

We actually did the same thing for Kongregate. Except we gave out an invite code to everyone who asked - usually same day. So the artificial scarcity was... artificial. But if we'd had a big problem we could have stopped the invites. We did that for about two months and then took the invite barrier down. Worked for us. edit: I forgot the second half of this story. A few months after we took the invite barrier down, we decided to do a "Hollywood" launch - really all we were doing was changing the "alpha" to "beta" and releasing some new features (earning cards by playing games). It worked, we got lots of press. Fox News even called and asked if I could go on their afternoon cable show. I did (here's the video - http://tinyurl.com/2gpz7x http://tinyurl.com/2gpz7x). Our site immediately cratered - it was a much, much bigger surge than Digg. We got it back up in about 20 minutes and the follow on traffic was good as well. So I guess we did a hybrid Gmail/Hollywood.