In my recent memory, I really liked the way Quora executed on the whole closed beta thing - skim this for more details http://techcrunch.com/2010/03/28/quora-ha

In my recent memory, I really liked the way Quora executed on the whole closed beta thing - skim this for more details http://techcrunch.com/2010/03/28/quora-has-the-magic-benchmark-invests-at-86-million-valuation/ http://techcrunch.com/2010/03/28/quora-has-the-magic-benchma... Also, http://www.forrst.com http://www.forrst.com has an invitation only approach going on and I think it works really great for a community like that which self-selects. It really depends on the product you're working with. If the general excitement around it is high, you can do the invitation/referral to get more people interested like Dropbox and Gmail did. The Closed Beta idea also works because it gives some time to work out the kinks and have time to scale up (in the case with Greplin.com).