This thread from back in February discussed the duration of the sandbox and in particular a site of mine that had just come out after being there for about 14 months. [webmasterworld.com...]
About one week ago the site plummeted in the rankings after enjoying a period of reasonable traffic. The only significant thing that I have done to the site recently was to gain a link from a PR7 site!
What you are saying is probably true but this site was without doubt affected by the sandbox "effect" for more than 14 months. I rode it out until it was released a couple of months ago then I watched as traffic and rankings started to build up as I would have expected them too.
I am not implying that it is back in the sandbox and I also think that I have just been unlucky in an update. It has happened before and it will happen again.
There was a bit of discussion around this site in previous threads so I thought some of those who had participated previously were entitled to this feedback.