GTK is probably the main reason Gimp isn't a serious competitor in professional work, then. I can imagine what monumental task it must be to maintain a cross-platform GUI toolkit, but it's IMO the single most important aspect of Gimp. Let's face it, all the features are there. Maybe 5% of Photoshop's deep ocean of features is actually used by the average user, Gimp can provide almost the complete functionality. Some extra performance and nice-to-have tweaks might still make a difference, but they're not what's holding people back from considering a free option over a several-hundred-dollar one. The user interface is what's crap. Sorry, GTK, it just is. Copy-pasting what I wrote a few months ago:

>Out of curiosity, I tried installing Gimp to see how much has changed (for the better?) since I last checked it out. The tool interface doesn't quite fit into its window by default so you have a tiny little scrollbar at the bottom that you have to scroll to see the full text. I resized it. After popping out a submenu, it once again didn't fit.

This is plain unacceptable. Yes, this is 99% there, it's a minor thing, it's probably thousands of man-hours to avoid a gazillion other bugs and issues and even get to this point. But it's not enough. A UI for such a tool, where you actually fiddle with it a lot, has to be perfect. Perfect on a technical level, perfect in a Apple-y "let's ensure that the empirically determined most-used features are shown first and less-used stuff doesn't clutter precious screen-space" sense that takes long and frustrating trial-and-error involving real-world feedback. You can't have a button that's 15 pixel larger than it has to be. You can't have a layout arrangement that wastes half a window because it's poorly aligned. You can't have spacing that's inconsistent enough to make you hesitate clicking an icon because you're not sure if it's connected to some other element of the interface.

Open source/free software needs a user interface push, but apparently that's not a sexy field to work on.