It would be great to hear everyone's views based on their experiences on this question ...

Also, what other factors can help a site in getting out of the sandbox?

This begs the question "does the sandbox actually exist"?

I think it's generally presumed that the sandbox doesn't in fact exist. And even if it does, just ignore it and work on making good content and getting noticed and getting links. That's all anyone can do, unless you own the majority of Google.

Time!

The sandbox is nothing more than the natural effect that occurs when new businesses or sites attempt to establish a presence. They make mistakes, they worry about things they shouldn't, they head down the wrong path, eventually they put it all together, they head down the right path, and *click* light switch.

It's not really about quantity of links or Google PageRank or the alignment of the planets or (insert bizarre SEO myth here). It's about, as Alan said, working on content and telling the right people.