Frequent crashes to desktop after 1.4.6 update

Game crashes to desktop after a random interval. Sometimes as little as 5 minutes, sometimes as much as 12 hours. I can discern no pattern in what causes the crashes to happen. I've tried every combination of video settings, upgraded my Nvidia drivers, upgraded Java to the latest version, but nothing helps.

Prior to the 1.4.6 update, Minecraft was rock-solid. The crashes started happening soon after the update, and I haven't changed anything else about my system.

About every 1 out of 4 crashes, I get an error log in the folder where my minecraft.exe resides. I've attached a few of those.