My Xp1700 has been ran at 2500Mhz a week after i got it, and stayed there. Only retired it a few weeks ago...
Electromigration Does happen, but with the upgrade cycle of the average poster on here, it soesn't make a difference. Even I, who lags quite a bit behind bleeding edge, won't see that effect. As long as you are sensible (less than 1.6v into most A64's will be fine), and have decent cooling (<50c), then you'll be fine. Tell your friend to read up some before he starts spouting carp.