Clearly got to be Butter Face.
I've still not got my head around a potential Windows 8 roll-out here in this School. I can't get the tile start menu doing exactly what I want for user profiles.
Gimp's not that bad any more. Certainly no worse than Photoshop, which was always pretty dreadful. Illustrator has a decent interface though, whereas Inkscape is just... yeah, bad.
GImp, though much improved, is certainly still much worse than Photoshop*. My biggest complaint about PS is that all the stupid do-dads they've bolted on since about version 6 should be offered as optional plug-ins. And the drm and now cloud bullshit.
But the interface is actually about as good as it gets for such a complex and powerful set of tools. There's loads of people (mainly professional photographers) who only need to perform a few rote enhancements to their boring pictures of weddings, corporate smurfs and hamburgers. So for them the GUI and learning curve could be significant drawbacks. But hey, that's what instagram is for.
* full disclosure: I love using gimp.
I guess I put up with Inkscape (and its bad performance on the Mac) because it's the only vector drawing thing I've found that has a decent amount of features. I forget what exactly but I looked at several and they were all missing some obvious feature that I use a lot (and by "a lot" I mean "a lot on the rare occasions I actually need to use a vector drawing program").
And as to Gimp, well, no Layer Styles = no good tbh.
Pro photographers would probably do better using Lightroom if they're only doing rote enhancements. Way quicker.
Windows Ain't. It sucks. :-(
One thing I really like about Inkscape is that it's quite powerful for doing conversions and stuff on the command line.