http://www.seochat.com/c/a/Google-Optimization-Help/Google-Sandbox-Frequently-Asked-Questions/
http://www.storebuilder.co.uk/article208.html
I don’t know if it exists or not, but I do think there is some sort of penalty for newer sites. Rankings for a keyphrase that’s not too competitive – I have a top 5 positions in Yahoo&MSN Beta. Plus top5 positions for any allinX commands in google. Yet google doesn’t show me anywhere.
So where or not it exists is debatable, but there is definantly some sort of filter going around.