Ubuntu on a laptop was too much of a CPU hog, which is why I use Crunchbang now. Ubuntu, at idle on my laptop was about 20-30%, Crunchbang is 1-2% idle.
Kernel, drivers, daemons, services, desktop managers, applications, GUI clickety clap crap. Pay attention to what actually consumes cycles. GNU/Linux distributions offer varying collections of stuff, but you don't need to limit yourself to the default. I've gotten the impression that there are myriad of different Ubuntu variations out there.