Steve--
I have a USRG30. Although I've never made any adjustments to the neck, here's what I remember hearing when I asked around:
Use the hole in the back of the
neck joint to adjust the bend of the neck.
Do not use the hole on the bottom of the neck by the 15th fret. That could theoretically cause your headstock to fall off!
--Brent
(Edited by bduersch at 1:00 am on Dec. 26, 2000)