After installing the 10.5.5 update for my Macbook, I noticed both wireless and wired internet access seemed slower. My wife's Macbook, running 10.4, didn't have the same problems.
I did some poking around the internet, tried scanning for a potential Trojan horse (none found), and finally decided to try turning off IPv6 for my ethernet connection (Go to System Preferences -> Network -> Advanced options (on the ethernet options screen) -> Configure IPv6 -> Off). When I rebooted, the problem was gone.
Has anyone else had the same problem? What was your solution?