Speaking as a visual arts professional, GIMP won't do as a replacement for Photoshop for me. In addition, there's no replacement for After Effects, and no equally good alternative (IMO) to Premiere as a current-generation video editor.
I take it the difficulty of making these apps work in Linux is basically impossible?
I've just looked through WineHQ, and my understanding is that even on CS5, After Effects doesn't work at all, Photoshop is fairly buggy, and Premiere doesn't work at all.
I've also noticed that Gimp makes jpgs of lesser quality, smaller, but noticeably trashier.