Upgrading to or installing Quicktime 5.0 adds a little program that runs automatically from your registry called qttask.exe. It does not appear in your system tray, but it launches automatically and runs in the background. You can see it when you run task manager (ctrl-alt-delete).
This little gem supposedly "checks your registry for new QuickTime associations." But it clearly has some "undocumented features." It is, in fact, an internet packet sniffer that will totally trash your AH performance. God knows what it is doing (perhaps looking for QT video?). Apple spyware? Al Qaeda terrorism?
I am blessed with excellent pings (<50ms) to the AH server, and always had pretty smooth play, but after installing QT 5.0 I noticed weird stutters on my front end that had not been there before. Several folks also complained I was warping (even when I wasn't "stick stirring," hehe). Recently, I just happened to look at the processes I was running [ctr-alt-delete] and saw qttask lurking there.
If you are running WIN98, you can click start>run, type in msconfig, hit enter, click on startup options, and uncheck qttask.exe
Otherwise, you may need to mess with the registry and delete the "run" key that mentions qttask.exe. I would not recommend doing this unless you know exactly what you are doing [insert lenghty legal disclaimer here]. Just deleting the executable from your windows/system directory will give you an annoying message every time you boot.
I did a little internet investigation, and other online gamers have mentioned the pernicious effects of qttask on latency.
Anyway, stopping qttask from running in the background made a world of difference for me.