I just massively speeded up web browsing on my MacBook Pro: I removed the Domain Name Servers (DNS) from the TCP/IP section of the Network preferences.
A couple of weeks ago a friend was using her Windows laptop at my house. We both visited the same page at the same time. Hers finished loading while mine was still thinking about finding the page. That was pretty annoying and embarrassing.
Today I have a friend visiting from out of town. She has a G4 PowerBook. Same thing happened: we both visited the same page and hers had loaded while mine was still thinking about it.
As an experiment I removed those DNS servers and saw an immediate and dramatic improvement.