OK, if you have two nics on server A with crossover cables to two nics on server b, it will be no different than if they were connected with a hub, bridge or switch. They each need their own small IP address nets. Then, why should IPMP care what the network fabric is?

I am not personally experienced with crossover cables. I heard that it can be hard to get them to behave if one server is powered off, but perhaps some nic firmware has stepped up to this. It seems like a frequently overlooked inexpensive and fast network fabric, with no collisions and in full duplex with not much length limitation. NICs are cheap, and wire is far cheaper than gigabit switches! You might run out of slots after a while. There is much need for this sort of bandwidth with high performance SAN and RDBMS client-server configurations.