Kevin Burton rightly thinks stealth mode doesn't work (emphasis mine):
If you think your idea is valuable you're wrong… Good entrepreneurs don't create ideas — they execute. It's all about execution…
Here's the important part. One major component of your execution strategy is going to be convincing the blogosphere that your company is the next big thing and will change their lives. You can't do this when you're in stealth.
Stealth mode also prevents you from hiring engineers, finding investors, and partners. There may still be a few small reasons why going stealth is a good idea but I think for 95% of new Internet companies it just won't work.