my AR7s from last year (still skiing them) have about 50 days on them as well and I have 5 edge cracks, but no signs of then worsening. I ski them like 80% park though so they get beat. interestingly enough my AR5s from 06 and AR6s from 07 are in better shape edgewise
I have hit rails with them. compared to previous skis i have had, these ones have a lot of sections where there are gaps between sections of edge. Compared to my suspects the edges dont seem constucted very well.