I was on my lowbie rogue killing boars outside Orgrimmar when I noticed that I was still gaining skillups from mobs that we're grey to me in skinning. I then went to hillsbrad and noticed the same on skinnable mobs there. Apparently skinning will now level up from any mob skinned. I'm in the process of levelling my 85 to 525 skinning on level 6 boars.
Basically
1. Kill any mob
2. Skin it (Even if its "Grey" to you)
3. ???
4. Profit! You will gain 1 skinning skillup no matter what level the mob.