I'm a long-time GIMP and linux user. I was having banding issues with GIMP and believing them to be an 8-bit problem I decided to give Krita, a 16-bit program, a try. For me, Krita was unusable. Any layers I added to the program resulted in 10 to 20 second processing delays, or more. I've never had such problems with the GIMP, where I commonly use at least a dozen layers. Also, the cloning tool is not like the GIMPs, and with the processing delays it becomes an exercise in frustration to clean up dust and hot pixels.
FWIW, I use a Toshiba laptop with 2-core 64-bit AMD processor and lots of memory, running KDE on a 32-bit Gutsy Gibbon linux distribution (Kubuntu). It's not a light-weight machine and all of KDE runs very smooth on it.... except Krita. The program has lots of potential but until they get a handle on its voracious consumption of resources, I'd stick to the GIMP if you don't need 16-bit processing.
-Al Andersen (first post)