I like stock which is why I am not running a rom. But being rooted offers apps and features I can not get with an unrooted phone. I am running a stock 2.1 that is rooted not only for o/c but for the wifi tethering apps, the ability to use spare parts, which really improve your phone performance. You can switch transition speed from normal to fast and that alone add speed to your device.
I am tired of roms that just f/c (not saying all roms do) so I just rooted and left it at stock, added chevys kernel, and spare parts. At 800 it runs smooth, cool, and fast.