Actually, I also thought for it, and once made an option for vertical top bar. But it creates problem with scrolling (with vertical scroll bars of windows). A possible solution is to make something like windows taskbar, which occupies the whole vertical/horrizontal space where it resides, but for topbar, there is no reason to waste so much space on the screen. What do you think?
Anyway, the skinning option will be great! Nice idea indeed... I have another idea. We can made two mode for topbar - Simple & Full. The simple mode will have only the keyboard mode changing and closing buttons, which will occupy a very little area on skin, and novish users will find it useful. The full mode will have all (like now). There will be easy switching between two modes. Vote for this....