It's all about disk speed
Recently I upgraded to a 10,000 rpm drive in my desktop and a 7,200 rpm drive in my laptop. Quite frankly this is the most cost effective way to improve performance on any machine. CPU speeds have grown dramatically over the last few years, so has memory capacity and CPU to memory bandwidth, but disk seek speeds and disk transfer rates have grown much more slowly. Chances are your CPU spends most of its time either idle or waiting for the disk drive now.
Windows Vista was designed with assumptions about us all having faster computers, more memory and bigger disk drives but without faster seek speeds and higher disk to memory performance, any move towards 'bloat' is going to result in a more sluggish computer with worse battery life.
Personally I run Windows 2003 Server on all my computers including the laptop - it's the most stable OS Microsoft has ever shipped and, to me, stability beats features and flashy UI.