Artificial scarcity is a great technique to generate excitement for a product while also limiting growth to a rate that won't melt your servers. We worked through a huge number of problems and early users gave us some of the ideas that have defined GitHub. By doing a Hollywood launch, things would have been very different and I am convinced, very much worse.
Do not, I repeat, DO NOT underestimate how much your users will help you to define your product. If you launch without having significant user feedback time, you've essentially thrown away a massive (and free) focus group study.
Let me also say that when we finally did our public launch, there was plenty of buzz, and all of it was the RIGHT kind of buzz. The buzz that attracts real, lasting customers (and no, we weren't on TechCrunch, that traffic is garbage).
Those early users are amazingly important. The overly passionate verging on stalker types that IM you asking if you just changed the color of a link and then tell you exactly what they think about it.
It was a similar story with Mibbit, although I didn't bother with beta, just threw the site up there and started iterating. The growth isn't quite a hockey stick, but it's extremely consistent which means I can grow the product along with the userbase.
Also I agree about techcrunch type traffic. Early on with Mibbit it got to the top on proggit. It was sort of fun, got a reasonable number of people in that night who looked around, said this is cool, then went... never to be seen again. Next day it was pretty dead. I think that's pretty typical.