The sandbox is a kind of filter implemented by Google in March 2004 that applies to maybe 99% of all new sites.
It's function is to push down new web sites in the SERPs.
My theory is that it was Google's solution to stop new spam sites that was created to rank high in the SERPs. It took probably some time before the Google spiders could detect such as a site and ban/penalize it and by that time the creater probably made several new ones.
When this phenomena was first noticed in March 2004 it was seen that it could take two months before a new site was "released" and could rank normally again. However by now October 2005, a time of half a year or more is normal and as long as more then a year has been reported.
By my own observations I have seen in Google that new sites can rank unusually high in the Google SERPs for some weeks before the sandbox filter gets activated.
