I've done it with the Gimp. Performance wasn't bad actually. Of course, I was on a semi-dedicated 1 Gig Fibre line at the time.
I had a P-II 350 workstation with 256 Meg ram, and a Dual P-III 750 MHz machine with 1.5 Gig of ram, and was editing a HUGE (100Meg raw) file.
I went from 40 to 50 second load times to 3 seconds.
This was back in the Red Hat 6.2 days, and I didn't have to do anything other than ssh in and start the gimp to get it to work. That same weekend, our Windows SA spent about 20 hours getting Windows TS set up and running, and was bragging to me how cool it was. All the while I was sitting the saying, "uh huh" and "yep" while editing the picture. When I pointed out what I was doing, it took a while for him to accept that all I'd done to make it work was ssh in and run the gimp. 🙂 Poor guy.