What I do know for sure is Asus, Gigabyte, and Asrock claim their existing Z68/P67 boards will all be able to run Ivy Bridge, although they will require a UEFI update.
Only Z68/P67 boards marked as "PCIe Gen3" are guaranteed to be able to run at full speed (PCIe3). Some older boards may run at full speed, some may not.
When I buy Ivy Bridge, I will also be buying a Z77 board anyway (most likely another Asrock), and my existing Z68 with i7 2600K will be used in PC 2. I won't be selling the Sandy Bridge system I have, as i'm very impressed by this processor.