I didn't see this posted anywhere, and I didn't notice it in the Bestiary Errata, but it seems to me that the Gnoll's Perception score (listed as +2) should actually be +5?
They only get 2 skill points (2 -1 for Int x2), all of which have gone into Perception, and they get no Wisdom bonus for it. Yet, as I understand things, it should be considered a class skill for them, and they should get an additional +3 to it, correct? That seems to be the way it works for other creatures (such as the Bugbear).
If you look at the description of the humanoid type in the bestiary, perception is not a class skill for humanoids.
Aha! Thanks for pointing that out. I see what I was missing (and I noticed they errata'd the bugbear, which accounts for the other discrepancy I was making between the two). :)