Go to ebay.com and search for the word "gmail". There are 221 of them on sale. Currently, the highest bid for a gmail invitation is $150 US. Meanwhile, most people have already just given their two invitations away to friends. I'm pretty sure that this alleged "beta test", as they call it, is really just an elaborate advertising scheme because it's pretty much working fine already. The goal is clearly to make gmail a very fashionable, high-demand product in advance of the official release.
Looks like it's working well so far.