well...you can't rearrange anything or phyically size anything down, but you can go check out my UI skin...i tried to pull out all the "frills" and leave just a simple UI...
if/when we can start actually editing the UI as a whole, instead of just the images, i'm sure you'll see a lot of minimalist UIs popping up.
i know Nui(Bossy Ed.) will be getting a facelift if it happens! :P