I personally am not interested in RAW processing programs, but I would really like to remove Adobe products from my girlfriend's computer.
Fromm what I can see DigiKam + GIMP' seems to stack up quite well against the somewhat industry standard Photoshop + Bridge combination for professional photography. I think if you can learn how to use the GIMP well enough then you could *realistically* use it professionally.
Setting up cameras for doing RAW editing on Linux is much easier than Windows due to DCRAW which from my experience (she let me play for a few minutes) 'just works' with professional level cameras. Plug and Play, no fooling around finding and installing the right plug-in from Adobe.