I've been looking into moving dalvik-cache to sd card, specifically to an sd-ext partition as ext3 (I think). I have the partition, but am stuck on the rest right now. I'm going to try again tonight maybe to figure it out, because this too is super annoying to me. If I have any luck I'll post back. I was hoping someone here has already been successful with it so I didn't have to kill my brain trying to understand it.
As it stands right now, moving dalvik-cache from /data to /cache is pretty easy (or can be). Just create a symlink at /data/dalvik-cache pointing to /cache/dalvik-cache. There's also a way of creating an actual link in the boot.img that points directly to /cache/dalvik-cache, which I think is where the change needs to be implemented in order to move it to /sd-ext. Maybe. I really have very little clue, but might as well give it a try...