I came across a post in the Advocates-only forums by Matthew Brown that indicated that Guild Wars was running better with recent nightly builds. He had recommended build 070713, but I figured I'd try the most recent so I downloaded and ran build 070724.
He's right! The Catacombs area which gave me so many problems before works much better now. Using the command line options recommended on the Tips & Tricks page (-dx8 -windowed -noshaders -dsound) I was able to make it half way through the Catacombs without a freeze. Previously the game would freeze immediately upon entering the catacombs. There's an area in the Catacombs with a waterfall where you first encounter spiders. It seemed like the act of looking in the direction of the waterfall precipitated the freeze. I tried reconnecting, but with the "-noshaders" option this time, and was able to get all the way down to Oberan the Reviled without incident.
The other surprising improvement: I've got battle sounds! I never heard those before.
For those who have access to nightly builds, you may want to give a recent build a try. For those who don't, it looks like you've got something to look forward too in the next release.