Battleground gear seperation is live. The check includes all gear available, both in bags and in bank.
Fresh level 80's and those with a bit of gear should have better quality matches from now on if enough similair geared players are in the queue.

Note that its a first implementation of the system and we will tweak it along the way.
I apologize if this has been answered already and I have just missed it but does this include the TBC realms too, or is this BG gear seperation purely for WotLK servers?