Yeah, each machine has its own worker assigned, all pointed at  stratum.bitcoin.cz:3333

Just confusing that the 30 MH/s working was working fine until 3 days ago...  The two that aren't working probably have the same external IP, as they are part of a massive university network. GUIMiner shows them hashing, just not earning shares. How can it be that they connect to stratum but don't earn?