well, after a month of the U9000 ROM working wonderfully, it seemed to eat itself (whatever programs I would run would instantly close). Went into CWM to clear all the respective memories and re-install this rom from the zip file. ROM was reloaded, rebooted, and sat there at the motorola logo for half an hour.
Okay, hmm, guess that isn't going to work. Good thing I have actual backups! Woops, no I don't: MD5 checksum mismatch on every CWM backup I have, including my backup of the stock rom.
Downloaded a CWM backup of someone elses stock, which passes MD5 but hangs on "Restoring system..."
well, this is great. I think the phone is just dead. I don't see how it could possibly be the ROM's fault. Hardware failure, manufacturer's fault, warranty time, but CWM loads so there is no chance of them not figuring out it was modded when it failed.
finally, okay, CWM successfully installed this from zip:
[ROM] MTDEV-UNROOT [final]
And now get an image of the green android with an exclamation mark-sign above his heat, presumably denoting the "dead" status of my phone. No boot loader will load, but it no longer looks modded so I think I'm fine to return it for warranty replacement now