The XLNTsolution weblog has a whole stash of system tweaks they recommend to speed up Ubuntu Feisty Fawn.

Some of the tips include disabling IPv6, enabling parallel boot processes, reducing the load of the swap, and re-aliasing the localhost — and that just scratches the surface. Some of the tweaks are pretty advanced, but a good chunk of them are quick, easy, and should produce a decent speed boost on any system. The tutorial is specificially written for Kubuntu, but most of the tweaks will work fine in Ubuntu and any other Linux distro.

Feisty Performance – “Fly Like A Butterfly” [XLNTsolution via Stone's log]