I've still not managed to get a connection at any of those host addresses with Guiminer/Poclbm. Just keep getting (with all 3):
2013-04-17 17:41:32: Listener for "Slushs": stratum2.bitcoin.cz:3333 17/04/2013 17:41:32, no response to getwork, using as stratum
2013-04-17 17:41:42: Listener for "Slushs": stratum2.bitcoin.cz:3333 17/04/2013 17:41:42, Failed to subscribe
2013-04-17 17:41:44: Listener for "Slushs": stratum2.bitcoin.cz:3333 17/04/2013 17:41:44, IO errors - 1, tolerance 2
Edit: OK on stratum.bitcoin.cz with two workers now. I'm assuming it's just being super spammed right now. Slush, you're the man!