Why are people still talking about this sandboxing effect. I have never seen any evidence that Google is sandboxing anything based on newest of the site or its links. The thing I have noticed is sites new and old are filtered (or greatly reduced in ranking) from the serps.
It seems not to do with age but is more a factor of where the links are coming from. In my case I have sites that were filtered and others that are not effected. The non-effected sites generally have more links and links from a greater variety of independent sources. I noticed that sites that I network are filtered and do not benefit from this time of linking. I still network them I do so for the visitor and not Google. I don't believe Google should have the right to say who and what I link to.
However, this attitude doesn't solve the problem. The only thing that trully works is build links with non-affiliated sites. All evidence I have seen points to Google placing increased emphasis on local rank and athority status of sites and much less emphasis on page factors and internal pr (this is pr from within a site or network of sites).