Google Sandbox

The Google Sandbox is a way for Google to slow down new emerging sites. The Google team believe that new sites can not gain high search engine rankings almost immediately after their launch. New sites first have to prove themselves before Google will give them a good listing. The time a new sites stays in the Sandbox varies from 2 months to a year. While in the sandbox Google already spiders the new site and calculates page rank, but it keeps the Pagerank 0 for the outside world.
Some clever people made the best of this system by optimizing a site a couple of months before  they believed searching on the sites keywords would become popular. For example the movie industry.