I am looking to upgrade my 5D MK I for some time, I am quite tempted to switch to Sony. I like the translucent mirror concept. However, as pointed out in many reviews, one of the problem is the small buffer size. I don't really need 12 FPS, 8 FPS is enough, but I hope the translucent mirror technology can give more accurate continuous focusing. And I like the continuous focusing in video too. Also, the in body stabilization and Carl Zeiss lens. If Sony can do well in the PQ including high ISO noise, I think I will switch. They also price it quite aggressively, I think.
I am waiting for both the 5D MK III and Sony A77 ... or even next Nikon D700. But please, don't give me a 30 Mbp sensor ... I don't need it.