Sandbox Effect is causing new web sites not to rank very well in the search results of Google, not even for the least competitive phrases. It usually means that a filter is being placed on new web sites and cannot rank very high for most words or phrases for a certain amount of time.
There has been a lot of debate as to why Google uses the sandbox filter. However, it is believed that this is an attempt by Google to discourage web site owners that uses SEO Spam techniques or some call it as blackhat technique to rank high fast and make a quick buck before Google discovers it. This is largely because Google uses link popularity so much to rank web sites in it's search engine.
There is no way to know for sure if a new web site is in the Sandbox, but the best way to determine if you are in the Sandbox is if your web site has a good amount of quality backlinks, quality content and a good ranking on other search engines, such as Yahoo!, MSN and Ask Jeeves, but still no where in Google's search engine results for your keywords.
It is a common trend that it can take up to 6 months before a new web site can get a high ranking in Google's search engine results and out of the Sandbox, but this varies from web site to web site. It also depends on how competitive your new web site's market and keywords are.
There is no known way of speeding up the amount time a new web site is in the Sandbox. But some new websites tend to get away with it by doing some tagging through social bookmarking sites. Some would even buy links from blogs or sites with high PR and were able to be crawled by SE spiders earlier than expected.