MMO Crunch has discovered the perfect solution: 5-Minute MMORPG.
It's a simple, cute flash game that promises level 80 in five minutes, offers exploding opponents, turns lag into a feature, and is easy enough to allow you to pick up the basics on the first try. At ten players per map, it's a bit on the skimpy side for an MMO, but it fits with the general theme of quick and streamlined. The ironic humor certainly helps the fun, as well.
The game is free, requires no download, and is a surprisingly fun MMO-lite for those who want to play but are short on time.