As a follow, in case any of the posterous guys are listening, Max and I played around a bit and could not replicate the error.

My current guess -- it's not my problem so all I have is a guess -- is that under heavy load, posterous fails to resolve the blog name and instead takes new users to the splash page. This may be a scaling problem, or it could be random pestering. From a user's standpoint, it looks a lot like pestering.