A thread over in the Google Webmaster Groups talks about the Google Sandbox, and about 301 redirects. In this thread, Adam Lasnik jumps in and sets some expectations on the handling of 301 redirects, and also does some myth breaking. Here is what Adam has to say:
1) There’s no universal/intentional sandbox. But, as Matt has noted and MRG has quoted (hey, that kinda rhymes), there are algorithms which have a sandbox-like effect on some sites.
2) 301s pass PR and related signals appropriately. Usually takes a couple of weeks for things to smooth out, though.
Most advanced SEOs abandoned the notion of the sandbox a long time ago, and now focus on the process of building trust in their sites (or getting into the trust box).
But confirmation from Google on the speed at which they handle 301s is new (to me at least). This confirms what we have seen in our own experience.
About 15 months ago we took a site with about 20,000 pages and we moved every single URL on the domain, except the home page. It was a massive move, and potentially a very costly one, as the site drove most of its revenue from organic traffic from Google.
The site made the move within 2 to 3 weeks. In that timeframe, the URLs Google was showing in their index had all updated to the new URLs, and the rankings of the pages were completely in line with the rankings of the pages prior to the move. This was great stuff.
However, as I noted in the Google Groups thread above, a massive move like the one we made does come with risks. I would not do it unless you really, really, really need to.