How long you got your domain registered for?
I hear if you have it registered for three years or more, Google thinks that the website is going to be used for a good purpose, where as sites that are only register for 1 or 2 years are more likely to be ditched after 1 or 2 years and therefore are more likely to be sandboxed.
It may be bull, but its funny how when ive register a domain for 1 year, it quickly rises to the top page in a couple of months and then within a couple of weeks completely disappears into the sandbox.
And when ive registered a domain for 5 years its never go into a sandbox at all.
Maybe a fluke, but i dont know.