Just took the public beta of...

Adobe Photoshop Express

...for a spin. This web-based image editor is free during the public beta phase. I have no idea if it will remain free afterwards.

I uploaded an underexposed cameraphone photo to test the image editor. The interface consists of a series of choices for each editing option (e.g., sharpen). Hovering the mouse above each option previews the change in the main window. Selecting the option makes the change permanent. It is very much a photo editor versus a general purpose image and drawing editor. It was reasonably fast. And, it let me download the modified image to my local hard disk. You can see my before an after example below.