..unless you drag it off the side toolbar and off the window that pops up while you are doing that, then you lose the thing totally. Gone forever. You can't find it in the palette again unless you reset the workspace.
I've also found that using the standard, non-themed UI is A LOT snappier. I'm using this in VMWare, and the UI performance had pretty much convinced me to give up. I had to click the menu and no move the mouse for 1-2 seconds and wait for it to "flick" it's 3D effect or whatever the heck it was doing otherwise whatever command I was near when it did that would happen and the UI was generally clunky and slow. Switching all that off and using the Standard UI it's like zip zoom zang. Done.
Customizing it is a bit trickier. You pretty much can't drag stuff around like having a theme on. It's a bit of a pain in the arse. Seems if I just pick up something and move it I have to name a new toolbar. Pick it up and move it again, I have to name another toolbar and of course I can't use the same name I gave it because well, that's taken. Even though it's only moving.
I can't figure out how to get rid of all the extra space and move whole groups of stuff, if I move each of those line/arc tools I have to create a new toolbar each time I move one. With the theme when I grabbed one of them - the rest of them came with it, and moving/reordering/etc. was all just as simple as sliding stuff where you wanted it.
But the smoother zippier performance outweighs that by far. Though it would be nice otherwise, to get back that inch of screen space on top.
The screen shot attached shows all the 'empty' areas in the palettes.