Using Ubuntu? Install dnsmasq and go faaaaaaaaaaaaast.
Want to make your browsing go really quickly? Unless your host is running bind/named itself, you can make it stop asking another computer (possibly over in your ISP) every time you try to visit a site or download your mail. Sometimes there’s a pregnant pause at it’s looking it up—again.
The dnsmasq program is really fantastic and keeps a local cache of the addresses you’re asking about. Your computer has its own local place to scribble down things you’ll probably ask for again soon.
Instructions for setting it up are also available on an Ubuntu blog, with the quickest steps in its first comment.
P.S. It’s not just Ubuntu, actually—you could put it on all sorts of systems, including Macs running OS X.