As a GIMP and Inkscape user I would like to see all the most used commands always on screen.
Like in Inkscape I might go from View > Display Mode > Normal - to View > Display Mode > Outline a zillion times - is there a toggle button for that?
Some of us remember the keyboard short cuts better than others...
Plus seeing the MOST USED stuff makes learning easy.
In GIMP, think about the commands that you use, doing virtually anything. For me that might be zooming in and out, for example - these hot commands are nice to be one click or slider operations that are IN YOUR FACE easy to find.
Toggling the GIMP interface to all act like one window or many so called "boxes" is a must.
Being able to custom place ones "most used buttons" in the MENU BAR helps on real estate but is rarely allowed.
All in all, very nice use so far of the screen real estate on your GUI design.
If that is a zoom slider - yes I like it!
The overall look is very nice!
...And nice job in Inkscape!
I like the tabbed images also.