Recently I've been suffering from consistently high latencies ranging well into the 400-800 range so I did a bit of checking what I could do to improve the performance somewhat and it turns out that blizzard is one step ahead of me.
Patch 2.3.2 which will probably be rolled out sometime tonight (CET) removes the usage of a networking algorithm (nagle's algorithm) and with a little luck this should result in rather drastic performance improvement.
Ironically the algorithm itself was designed to reduce the amount of overhead on a network connection dealing with small packets so the fact that this is now botching up WoW's connection to their servers is somewhat amusing.
For those of you less skilled in the art of computing be aware that there is a difference in performance and latency.
Check the little indicator on your default WoW UI and hover over it to see both your latency as well as your FPS (frames per second).
A high latency means networking issues which will hopefully see some improvements after 2.3.2 is implemented. A low FPS means your computer is having trouble displaying all of WoW's graphics.
There's a lot you can do about either one but since the networking stuff (latency related) is generally more complicated I suggest you simply wait for blizzard's patch team to make improvements in that department. If however you're suffering from choppy gameplay (low FPS) then there's a lot you can do in the settings menu of WoW.
Go to your visual settings and set everything to low that you don't need. Fancy weather effects, ground clutter rendering and the distance this clutter is visible from are things like that add nothing to the game and can be turned off.
If you're already running on video settings that are as low as you can possibly tolerate and find that your FPS is still terrible then go to your sound menu (yes sound) and turn off reverb and maybe even ambience sounds. Drop music too if you can live without it.
Other than that make sure you have as little other stuff running as possible in the background. MSN, Yahoo and various other messengers can be a drain on resources and if you can turn them off you will in most cases note a difference.
Also take another look at your addons. If you have a lot of addons then they eat a lot of memory, if you don't have a lot of memory in your PC then this will quickly turn into a bottleneck. Think about turning off addons that aren't crucial or see if you can combine a few addons / replace them with different ones.
I admit, the above is somewhat generic advice that probably has been posted a million times over, but there's nothing worse than choppy gameplay combined with high latency.
Cheers to patch 2.3.2 may you bring my latency back into the green and good luck to all of you who are having problems