This is just my $0.03 (damn inflation) and not the official opinion of the administration...
With that said, I would disagree with this idea. The AT Forums are first and foremost a computer help and discussion forum. When you're having computer problems or want buying advice right now (because it's burning a hole in your pocket), then you don't have time to be in a holding pen. People are going to move on to signing up at other forums where they can post right away. And while this would cut down on spammers, I'd rather take new members and spammers together than to give up the former to cut down on the latter.
I'm with ViRGE. The idea of the OP has merit, but in our case we are willing to take the handful of noobs who do spam in exchange for enabling many many more non-spamming noobs have much more immediate access to the forums they registered to interact with.
This is one case where we are intentionally "reactive" and intentionally NOT pro-active.
However, there is one case in which we are pro-active regarding enforcing a bit of a vetting process for new members and that is in regards to the FS/T forum. In that case a new member needs to post at least 25 posts and have been in the community for a minimum of 7 days before they gain access to FS/T.
The policy may change over time, we are an adaptive organization, but for now I'd rather cleanup after the few noobs if it means that many more noobs are unhindered in their access to the forums with which they are so eager to engage.