When it comes to annoying user interfaces, the GIMP is at the top of the list. Haven't you ever heard of a multiple-document interface? Or docking toolbars? Or any of these fancy things that have been around since at least Windows 98? I remember using Flash 5 and it had fancy docking toolbars. Why can't GIMP, a "modern" app, use a single window?
So I start it up and get this little panel. It's got some of the familiar things on it, like brush, eraser, select, etc. File menu is familiar, but what in god's name is Xtns? I guess with my computer savvy background I can figure out it means extensions (is that what it means? I haven't actually checked). So I create a new image. This opens up a new window (WHY?!?!) that lets me draw on it. Cool. So close that, I want to create a button from one of the extensions. I click Button->Round Button. A nice little thing to make my button. I can pick colours, padding, all this jazz. I click OK and three more windows open! Gah! It's like browsing to a porn site with IE6 and having a million pop-ups appear!
I haven't even really used Photoshop for more than cutting out pieces of other images, so I don't even really know what I'm missing. What I do know about GIMP is that the developers have done a wonderful job on the complicated aspects, but there's all these little things that bring the whole thing crashing down.