Migration doesn't copy Instrument Library
You know the Migration Assistant, this program that takes your files from your old computer to your new one so that everything looks exactly like you left it? Well, in the case of the new computer that comes pre-installed with GB, it doesn't exactly do it (or didn't do it in my case): It did transfer all the loops that I had, but the Instrument Library was the default one after migration, with all the added Instruments (like from Jam Packs) missing. I had to get it manually from the old machine. So this should be a warning to keep the old computer or a copy of it for a while after getting a new one!
iMac (27-inch, Late 2012), Mac OS X (10.7.5)