Another huge problem is that if I'm working with a "real" designer its exceedingly unlikely that they are going to have GIMP or be willing to learn it, and with

Another huge problem is that if I'm working with a "real" designer its exceedingly unlikely that they are going to have GIMP or be willing to learn it, and without pixel perfect rendering of PSDs (which it doesn't have) if I need to make buttons, etc I have to use Photoshop.