I'm mining at 670Mhash/s on deepbit, and I earn about 1 BTC daily. How much would I earn if I were to change pool?
Depends on the pool of course. But back of the envelope calculation you would earn 1.13 BTC at Continuum in pay per share mode. More in the regular pool but with a higher variance. Other pools will yield different numbers. Just run your hashrate against the pool fees for each pool.
You must have miscalculated something. If he is in PPS mode at deepbit, and changes to PPS mode at continuum, he'll get 1.056BTC.
Oh, and I wouldn't recommend slush's pool, as it doesn't support long polling (which basically every other pool does), so you'll get more stale shares, which means ~2% less income.