Sure, it was already possible (if complicated) to jailbreak a first-gen iPhone running the 2.0 software under Windows, but this is the one-click tool all you crazy cats with those extra G's need if you don't have a Mac -- too bad no one's come up with a better name than "pwn" yet. Please, people. Let's do better.
PS.- As usual, you run the risk of totally destroying your phone mucking around with this stuff, so don't say we didn't warn you.
Update: winpwn.com is down already, mirrors in the comments!