I recently read an article that Google filed for a new patent on a page ranking schema, which takes different things into account. One of them was the fact that they now check to see how long you have your domain registered for. If it's for more than a year, then they categorize your website as a site that will be around for a while and this plays into their ranking factor. However, I wonder with all the talk about the "Sandbox" theory, if Google is able to see how long you've had your site's domain registered for in the past and uses this info also.
I think that parts of the patent may be "defensive". In other words they registered all methods they could potentially use to stop themselves from being sued by other parties who could patent the methods in the future. I doubt that they use all elements of the patent, but if you only have a few domains that you are serious about developing I would register them for a few years. Also, I think their spam identification system is dynamic rather being based on set rules. In other words Google probably have a list of spammy sites, which they analyse for common characteristics. Then, if your site contains any of these characteristcs they would probably slap some penalties on it, such as the sandbox (whatever that means to you). The main implication of this would be that if at a later stage they find that the domain registration period is no indication of a site's spammyness, they would probably not bother to include it in the penalties algo.