All instructions and downloads are linked from my website at:
UPDATE 9/1/2011 1.03: completely re-written, includes one-click root and unroot for practically all Motorola Gingerbread devices, /system/app fix & restore, and ADB temp root. DROID 3 fixes work for build 5.5.959 (stock) and 5.6.890 (late August OTA update).
UPDATE 9/8/2011 1.05: lots of logic testing for fixing bad root attempts/root carry-over's for DROID X, DROID 2 Global, and other devices. Some messages were made clearer, and unrooting is now open to other devices (/system/app restore optional).
UPDATE 7/8/2012 1.08: new links for the system restore features
UPDATE 6/14/2013 1.09: guide re-written, files re-uploaded, everything should be working again (I removed /system/app restore feature since it wasn't reliable and now unnecessary with unbrick/restore methods)