I'm sorry, I was quite wrong. I forgot to reinstall the NVidia drivers on top of my new kernel. Now I am getting different behavior, though I can't say it's any better.
Now, instead of X crashing and giving me the output I mentioned in my earlier post, it just hangs with a blank screen. What's more, I can't switch to a different terminal using ctrl-alt-F1. So it's totally hosed at that point, and all I can do is reboot in an older kernel.