Q:

Do Mac Steam keys work for PC?

The Bioshock Infinite season pass (Steam key) is on offer at the moment, but only for Mac.
Having already bought the stand-alone game Bioshock Infinite a while ago, if I buy this DLC, will I be able to activate and play the DLC on the PC?
Essentially, what I'm asking is:

What is the difference (if any) between Mac Steam keys and Windows Steam keys?

A:

You will be able to activate and play the DLC on your PC.
As long as the game supports Steam Play there is no difference between Mac / Windows / Linux keys. 
I don't know of any multi-platform games on Steam that don't support Steam Play. However, always check before you buy.

