Seems dangerous and unneccessary to me. I've never driven a motorbike, but
their ability to overtake all stationary traffic means they effectively
carry their own bus lane with them anyway. Putting them in bus lanes will
encourage them to do 60mph, skidding into the side of all the idiot car
drivers who pull out of side roads ignoring what is in the bus lane and what
speed it is doing. A bus lane is a very dangerous place to be unless you are
driving a heavy vehicle such as a bus, London-style taxi or HGV.

http://news.bbc.co.uk/1/hi/england/london/7811062.stm