If you have read my coverage of the Coffee Talk with Senior Google Engineer : Matt Cutts you would have read;

Q: Does the sandbox exist? A: Matt said here comes the audience part? How many feel there is a sandbox? How many feel there is no such thing as a sandbox? SEOs normally split down the line. There are some things in the algorithm that may be perceived as a sandbox that doesn't apply to all industries. He knows it works to keep some spam out.

He confirmed basically that there is a sandbox like effect for some industries. Rogerd started a thread at WebmasterWorld named Matt Cutts on the Google Sandbox which confirms this;

In reply to a question from Brett Tabke, Matt said that there wasn't a sandbox, but the algorithm might affect some sites, under some circumstances, in a way that a webmaster would perceive as being sandboxed.

So, for some sites, in effect there IS a sandbox

Discuss at WebmasterWorld.