I have to admit that I needed a free photo editing tool a while back, I used Gimp for that task, and I absolutely hated the experience.
The UI is very Hardcore-Linux like, they try to clone something and add their own touch and mix Mac and Windows on the same box, and the end result is unusable in my opinion.
Since I've been doing only minor photo modifications lately, and I mostly shoot in RAW, I am very happy with Canon editor (not the photo studio or something, but the simple one) and IrfanView for high quality resize, sharpen. That's the only reason I dual boot to Windows + very rarely games.
Of course with new digital cameras, and more experience, there is no need to do per channel sharpening blurring and noise reduction, so maybe that's why I'm happy with those simple tools lately.
P.S.: Ok I just installed Gimp on my Ubuntu laptop, and after working two years in mostly Linux it seems a bit less hostile than it did few years back. But it still jumps at you unlike Photoshop.
Core 2 Duo E6300, MSI P45 NEO-F, Club 3D GTX 260, 4Gb DDR2-800Mhz, Audigy X-Fi Fatal1ty Champ1on ed., 0.5Tb+1Tb Seagate Barracuda 7200.12, 630W AXP, Samsung SyncMaster BX2450, ViewSonic VP171b