I'm not sure, but there's a few reasons not to post if you got accepted:

  1) just getting picked to go to the interview really only gives you like a 1 in 3 or so chance of getting in to YC.

  2) the news of getting accepted into YC is pretty
     noteworthy and shouldn't be squandered - 
    it's useful for PR purposes when you launch your product.  
    If you blow the news too early, you miss out on a 
    potential PR-based influx of users from TechCrunch for
    example.

Congrats to those who were picked to go to the interview!