Overclocking a 360 could be very useful.
The GPU is clocked at 500mhz... and should be scalable to 600-700mhz just like the X1900 GPU with some big air and proably could hit 820+mhz with phaze.
The CPU however... I have no clue, it's basically a regular Xeon, revamped with a third core and a new L2 memory architecture.
It should be able to hit 3.6Ghz... with some big air or liquid cooling, 4+Ghz with phaze.
mmm.... think of it... If M$ released an overclocking kit(which I'd soo buy) people could pwn PS3 with a tiny overclock, and actually run games smoothly at 1080
p with those crazy graphics we like to drool over.
Hell... they should release a whole slew of 360 mod kits and make the 360 capture everyone out there that likes to pimp-out their rig.