While I could, and still can get a superlative shave from a Fusion Power with a fresh blade for 2-3 days, after the initial "honeymoon" period, I am blessed with a lovely assortment of ingrown hairs.
I tried the Fusion as well and couldn't use it more often than ever other day without getting myself into trouble. I always got them right on the edge of my upper lip and d*mn did they hurt! The M3 was better - I could go for the workweek without problems, and the old Atra was even better. But since switching to straights I haven't had an ingrown in a couple of years - I don't think I've ever gotten one from a straight actually...