Mental,

First off, I freaking LOVE YOU!!! The convenience of having those toolbars contextually show / hide is fantastic. However there is one minor inconsistency that needs attention.

When you select a tool which has no sub-toolkit, could you have the "Select" subtoolkit display, but be disabled. This would prevent the panel from resizing, and throwing the document all over the place.

Alternatively, we could adjust the current location of the artboard within the canvas window, by and inverse amount to the growth / shrinkage of the panel ( but that seems entirely more complicated and no more beneficial )

Spatiality Rules!

-t