Polish users are waiting for Dual SIM support also I'm not sure about the percentage, but AFAIK number of dual sim smartfones in Poland is growing very quickly
I have an Acer Liquid Z2 Duo and indeed, dual sim support (SIM 1 = private, SIM 2 = work) would be a nice solution. Also here in Belgium a lot of people buy dual SIM cellphones.
Considering the growth of dual sim phones, I believe the usage percentage can only grow.
In Italy, where I live we have dual sims made by multinational companies such as those named in previous posts, plus NGM (New Generation Mobile). I would also appreciate this feature. Are you already working on that?