Kevin Rose unveiled a new project today, Pownce. Pownce looks like it's going to combine Twitter with the ability to send events, files, and links to your friends. Pownce allows you to send it to a specific person or share with everyone. Based on Leah's blog it looks like it's using S3 and of course AIR, the Adobe Integrated Runtime.
Pownce decided to do their desktop client in AIR because it was cross platform and they could use the web skills to port most of the website functionality to the desktop client. I think it's a pretty good use case for AIR. You can do everything you need to from the website and you'll never have to download the client if you don't want to. But if you become a heavy user of Pownce, you're going to find the desktop client much easier to use and a much better experience overall.
After playing with it for a bit, I'm excited about what Pownce is going to bring to the table. I'm a huge fan of Twitter and Pownce seems kind of like Twitter on steroids. I just hope they can scale. One of the amazing things is that this team has only 3 developers. With those three people they were able to build the website, the desktop client and hook everything together. That's the kind of thing AIR lets you do. If you'd like invites drop me an email. And I also need more Pownce friends.
Update: The invites are gone but I'll be sending more out as soon as I have them, so feel free to still email me.