Adobe's Photoshop Express, its free, online version of Photoshop is live right now. It's super easy to crop, adjust saturation or exposure, or perform several other simple, but solid photo tweaks, like pop color (pictured). You won't be doing any heavy lifting with it, since you can't work with layers.
You get 2GB of free storage in a quasi-Flickr setup, and it syncs up with Facebook, MySpace and Picasa—it pulls straight from your albums, and any saved changes show right up. Flickr syncing will happen in a couple of weeks.
One of the best features is that any change is reversible, and in any order—you can always go back to your original photo, or any step of the editing process. And because it's just a Flash 9 app, it'll run on any browser on Windows, OS X or Linux. Right now, it isn't integrated with Photoshop, like say, .Mac. But that's coming. A service aimed at pro users, with more storage, serious backup and other pro features is in the works, though it'll carry a fee.
Adobe Photoshop Express
Photoshop Express: Online Photoshop
Linear Mode
