My art staff does all my themes. Custom computers with an option for custom windows themes available nowhere else == teh g00dz.
We were also considering custom bootscreens, but neither SP1 nor SP2 allowed for those AT ALL. With the themes, all we have to do is put out a patch to reapply them after each SP, but the bootscreens require someone to hand-redo the damn kernel patches, not to mention the fact that the SP installers won't run with a patched kernel.