Unless you're living in a hole (or were at one conference or another last week, or don't care about digital imaging programs) you must know by now that Adobe Photoshop has released an online version called Photoshop Express. Sadly this isn't going to replace your software version anytime soon- it is limited in its tools and doesn't even let you work with layers...but for tweaking photos? Sure thing. You can also host some images on their site. Aviary has done a pretty thourough review of Photoshop Express against other online image editors.