Heh. I have spent way too much time on Wolfgang's Vault in the past several years. But before that, when I was in college I spent way too much time trading concert recordings via snailmail using etree.org. I mean, really... who has time for homework? :)
Once bittorrent became a big thing, sites like dimeadozen kind of took over the live concert trading on the internet. Another one that is pretty great is the Live Music Archive where concert recordings get put up permanently for download. The difference between Dimeadozen and the LMA is that the LMA only lets people put up recordings by bands that specify that it's okay to post their concerts, while Dime allows anything that isn't commercially available or specifically denied by bands (for instance, the Allman Brothers won't allow recordings of their concerts to be distributed online, but they're okay with mail trading).
A lot of concerts that are available on Wolfgang's Vault were available for years via etree and Dime. I know there were some legal issues with Wolfgang's that are hard to find any info about now that they've been resolved (Santana, Zeppelin and the Dead all sued a while back, but I haven't been able to find details about the issues). Between all those websites, you can basically find anything you'd like to hear, including some wicked rare stuff if you know what you're looking for. And quite a bit of it is really good.