I've just been playing with Bikehike, looking at some cycle routes in the Czech republic, and it's loading Bing in the window that normally has either the OS Landranger map or the elevation data in it. It didn't do this when I was using it yesterday.
I'm not sure how useful Bing is. I think it would be more use to have Open Cycle Maps in one window and Googlemaps in the other, for non-UK destinations.