Deepbit calculator says that you have to run about 500 Mhash/s to earn 1 BTC /day.... but! in less than 100 blocks difficulty will increase
using estimated diff, it only goes up to 554mh to earn one coin, so not to much of a decrease in coinage a day
mmm... diff will increase at 30% approximately.... 500mh+30%=650mh... not 554. Or i calculate something wrong?)