Yes, as I've mentioned GIMP's UI is horrible. And it's not because of open-source. Many open source UIs are equal to, if not better than, their commercial counterparts. This is especially true of large projects, which GIMP is. Unfortunately, the GIMP developers specifically have said "We like it this way and we don't care that everyone else doesn't agree with us". It's unfortunate, but the nice thing with open-source is that if other people want to, they can take the project, make a copy of it and redesign whatever they want to. And yes, this has happened to major projects before.

One piece of software you might want to play with if you're shooting RAW is UFRaw, a very capable RAW processor that has most, if not all, of the functionality of Adobe Camera Raw and similar quality. Definitely not as integrated, but you can still play with it.

Another piece of software that might be useful is Krita, which is another Photoshop competitor. It probably won't be available for Windows until the end of the year but it looks promising. The UI is also clunky (for different reasons than GIMP), but a brand new version is coming (along with the Windows support) so it might turn out good towards the end of the year.