I have an iGo Stowaway Bluetooth keyboard. This keyboard automatically 'goes to sleep' after a few minutes of inactivity. Pressing any key 'wakes it up' and, when it's paired with the iPad, resumes the connection.
I've noticed that, when the iPad is in 'sleep' mode (Autolock), if I press a key on the BT keyboard (when it's asleep), the keyboard wakes up and then the iPad wakes up too - and not just to the normal screen (where you have to slide the slider to confirm you really want to wake up) but straight into the full Home screen. So, if you have Autolock set to 'Never' it's a sure fire way to run your battery flat.