GIMP 2.7 actually has a single-window mode, which snaps the toolbars to the sides and has tabs. Unfortunately, it's a development release without any pre-built binaries for Windows, so, you'll have to wait until 2.8 comes out to actually use it (which will probably be some time this summer). I believe that GIMP 2.8 will also support OpenCL for rendering, meaning that if you have a graphics processor which exceeds the level of caveman, you will end up with exceptionally fast rendering times.
I don't see why people argue that GIMP is better than Photoshop. I mean, yes, Photoshop is $700 more expensive than GIMP, and I totally agree that for the price, GIMP is definitely better. However, it would be extremely silly to say that a free product is better than a $700 one; Photoshop is definitely superior to GIMP.
By far, GIMP is the best free image editor. If you're going to be doing pixel art, it's extremely overkill (and also more difficult to use), but for anything else, it's worth it. Paint.NET is terrible; I'm sorry.
EDIT: Raz beat me to it, mostly.
I don't see why people argue that GIMP is better than Photoshop. I mean, yes, Photoshop is $700 more expensive than GIMP, and I totally agree that for the price, GIMP is definitely better. However, it would be extremely silly to say that a free product is better than a $700 one; Photoshop is definitely superior to GIMP.
By far, GIMP is the best free image editor. If you're going to be doing pixel art, it's extremely overkill (and also more difficult to use), but for anything else, it's worth it. Paint.NET is terrible; I'm sorry.
EDIT: Raz beat me to it, mostly.