He's what they say about themselves:
Pownce is a way to send stuff to your friends. What kind of stuff? You can send just about anything: music, photos, messages, links, events, and more. You can do it all on our web site, or install our lightweight desktop software that lets you get out of the browser.
From the few minutes I've played around with it, it seems very Web 2.0, aka very cool. They look like to be trying to get into the Twitter / Jaiku space, but what makes them different, the ability to send files to your friends in addition to links and events. They have a Pro level account but that's $20 a year.