P.S. The only real difference is the fee charged by the pool. Slush charges 2% versus Deepbit which charges 3%. So over the long run, you'll make more with slush.
Other differences include long polling support and invalid protection. Additionally, latency between your workers and the pool can have an effect. Simply comparing fees isn't the only factor to consider. If it was, everybody would drop Slush & Deepbit to join BTCMine, bitcoinpool, Eligius, or my pool.
Great points!
All good reasons to not just go for the highest g/hash pool. Hoping around pools and then saying/thinking one makes more after a couple days is the worst way to pick a pool.