Thundgot over on the EU forums says there's a pretty drastic solution incoming to the busy servers incoming: Blizzard is going to offer free server transfers from high pop servers to low pop, so if you've really been driven nuts by all the queues and lag lately, this might be just what you need. On the other hand, don't jump into anything too quickly -- traffic problems are pretty common, especially when big patches (and, you know, expansions) come down, and odds are that once the expansion actually releases, things will die back down after a little while.
Of course, if you just don't want to wait, and don't have any particular ties to the server you happen to be on, then by all means, keep an eye out for the transfers. We're not quite sure which servers will be affected yet, but We Hate PUGs saw Quel'thelas on the list already along with a long list of high pop realms, so while we'll probably see more servers added to the low pop side, the high pop side there now is probably a fairly good indicator of the realms Blizzard sees as trouble. If you're on one of those realms and ready to transfer, sit tight and wait for the announcement today, help is on the way.