Back in June, beta users said that iOS5 will finally send track info over BT.
I upgraded to iOS5 last night and when I got in my car this morning is still said "BT Audio" and did not display the track info. I have a 2010 Mazda 3.
In another thread regarding Ford BT, someone reported that Ford has a Bluetooth update and after installing that, they are getting track/album info. So you may need to see if Mazda has an update, or wait for them to develop one.