My machine is based around that mobo and it is rock solid. The machine has been on without reboots for a month now. So far I have used it for some HD editing and transcoding.
Thanks to new Chimera v1.4 bootloader it is no longer necessary to use legacy kernel, SandyBridge vanilla kernels (10.7.3 and 10.7.4) work with no issues.
But why go with P67 when Z68 is out at similar prices?
New iMacs use Z68 so it's just logical there will be even less problems.
Check out the ASRock Z68 Pro3. Already some success stories here with it.
Don't know about Lion, haven't tried it yet.