I couldn't get this to work with my second card even though I can select it in the drop down menu.  I have three possible selections in the menu (cpu, 5770, and 6950) but only the 5770 will actually start mining, the others just sit there with 0 mhs.

This was as of last night, and I left my 5770 mining overnight.  I'll post again when I check on it later today.

I think this is a pretty cool idea and I hope you continue to develop it