The google sandbox is not something that google admits exists.
The symptoms are simply not getting google traffic – except perhaps for very obscure phrases.
It is not related to page rank.
Virtually all new sites will find themselves sandboxed.
Sites targetting competitive keywords/phrases, such as gambling websites are much more likely to be sandboxed than, say, a site about “my pet frog”.
The sandbox – which some SEO experts say doesn’t exist (yeah, right), lasts from 3 – 12 months on average. It’s primary purpose is to cut down on search engine spam.
From http://www.seochat.com :
If you have a new website which is sandboxed, the best advice to follow is to continue adding original, relevent content and to gather incoming links from other quality websites. It may shorten the sandbox period, and even if it doesn’t, when the site comes out of the sandbox, it will do better in the serps.