I tried a new free online photo editor today. It's called picnik and I think it has great promise based on the early returns. It is clearly not complete yet, as seen in the "Creative Tools" section where there are several "Coming Soon" buttons to go along with the Special Effects such as B&W, Sepia, Boost, Matte, Vignette, and Soften.
The screenshot above shows how I can easily grab my photos from Flickr (or my computer, or a website, etc.), edit them on the fly, and either save a new version to Flick or replace the old one.
Today I used the crop tool, the vignette tool, and the exposure tool. There are several other tools available as well. I look forward to the newer tools as they are released. As it stands now, it is a great tool for most of the very basic editing tasks. It's not going to replace a full-fledged photo editor anytime soon, but it is a great tool that is free, totally web-based, and user-friendly.