i don't know how many miles i've got on my pedals, but i'd guess well under 500. they're the medium quality Performance brand SPD pedals. they're my first clipless pedals, and when i got them i just tried to SWAG my cleats into a basically centered position.
they've been fine on rides up to about 20 miles or so, it's only on the longer (48 and 72 miles) rides that i've noticed the achilles pain...