I'm over 3000 miles (probably nearing 3500 at this point) on my 700 x 25 Armadillos on my road bike. The rear is extremely square but still not ready to be replaced. No flats since I installed them over a year ago. I've had a new set ready to go on for a few months now but the originals just keep on rolling. My plan is to replace them when I get my first flat with them. Otherwise, it's impossible for me to justify pulling off a perfectly good tire just because it looks funny.

I have over 1000 miles on my Nimbus Armadillos on my commuter MTB and they barely look worn at all. I imagine they'll last longer than the bike they are on.