Will 3.1 break any skins?

So far I have not seen any indication that it will, but since I am producing a number of custom skins in January / February and I will need to upgrade to 3.1 ASAP. its important to know if 3.1 will break any skins.

Probably depends on how you implemented your skins and whether you are upgrading from a prior version or installing new and then applying your skin changes.