http://bitminer.info/ 8 days ago:
5570: $2.20/day, 29 day break-even
6870: $8.19/day, 24 day break-even
today:
5570: $0.97/day, 69 day break-even
6870: $3.72/day, 58 day break-even
Definitely getting harder... and I just ordered a 6870!
(I don't know if the $ values are skewed by the recent mtgox problems...)