Port Fail-over

Isn't Cross-Stack Etherchannel link aggregation within a Cisco switch stack instead of two separate Cisco switches? I guess you were referring to "dual homing" BIG-IP to two separate switches.

I have a customer whom we helped to use two separate Nexus switches, with Virtual PortChannel (vPC), to dual home a BIG-IP pair with crossed LACP links and that works fine in this scenario. I assume Cisco VSS can do about the same. As Brad mentions spanning tree is not needed - and not recommended either..