Well, I successfully messed everything up. I had just gotten my 2.1 Droid rooted, WiFi tethered, and CPU overclocked, but of course I was too ambitious. I attempted to follow this guide to force YouTube to always stream High Quality videos, even over 3G. After rebooting the phone it infinite rebooted at the white "DROID" logo. I rebooted back into recovery mode, dig some digging, and found out that somehow (and I honestly have no idea how; I was very careful with the commands, and I'm very familiar with the Unix commandline) managed to remove everything in the /system/apps folder except for YouTube.obex. Crushed, I tried restoring via nandroid with no success. (Kept getting error 21.) I tried to redownload the 2.1 update, but it failed whenever verifying the /system/apps directory. I have been able to flash CyanogenMod, but I'd really like to restore back to the official firmware. I'm bummed that I lost all my user data, but if I can just get my phone back to stock (minus the SPRecovery, of course) I'll be happy.