Bonus: Try to draw a line in GIMP (without first going to google). Have fun! (;
Edit: In fact, I think GIMP and Blender have kind of opposite UI problems. GIMP tends to go along with the obvious toolkit defaults, making no concessions to usability, whereas Blender reinvents everything from scratch for efficiency, making no concessions to convention.
That said, Blender's GUI has been updated dramatically over the last 5 years. It is still quite painful ("discoverability" does not seem to be a concept they've become acquainted with), but in fact it's far better than it used to be. I'd made occasional attempts to acquaint myself with Blender starting in the late 90s and had invariably failed; tried again a few years ago and after a few days of pain I was being incredibly productive with it.
Most features can be found in Menus. Every clickable UI element has a tool tip if you hover.
With your mouse over the 3d port, hit the spacebar and fuzzy search for commands.
Most times there's a menu option there's a hotkey listed to the right... or you can right click a menu item and "Assign hot key."
You can also right click things and click "Online Documentation" for documentation on it.
Granted, I don't see an easy way to discover that "TAB" is for switching between edit and world mode when an object is selected... though you can switch modes in the "Object Mode" drop down 3d port menu. there's not a tool tip for it. ...and probably other things. It would be helpful if a better getting started guide/beginner walk through (like this introduction.) could be found in the splash screen and help menu easier.
Voilà, done (without using Google).
GIMP is not a paint replacement. Since GIMP is primarily a tool for image retouching and editing, drawing a line is not it's most obvious use-case.
> Blender is to 3D modeling what Gimp is to image editing what Darktable is to photo editing. Painful.
The main UI concern they have, is that they're usually not the first software of their kind people use. Switching from photoshop to GIMP is hard and people complain about the UI, but UI-wise, switching from GIMP to photoshop is equally hard.