sgolds, re mixed Athlon-64/Opteron dual system
Another reason why a mixed 2P system is silly is that, if the Opteron dies, you can't switch the Athlon-64 into its socket and continue working in 1P mode until you get a replacement.
Over all, just a silly concept when dual Opteron systems are going to be quite cheap (once Via and nVidia boards come out and we have a competitive market).