I'm at 24,750 and still have pretty good tread. Only the outer most tread is noticeably worn down.

mine wouldn't pass inspection anymore btw... not just because i liked the PSS :)

I got about 16k out of mine. The last tech to due an alignment on my Z forgot to tighten down the adjustment nut on my camber arm so specs were shot. Good thing I found this in time, I was all the way down to the cable.

http://i49.photobucket.com/albums/f2.../steelbelt.jpg
The tires were already worn prior to this, I would have maybe gotten 20k out of them if my alignment wasn't FUBAR.

For the stock Potenza's, I had 20,000 miles and my rears were done. Fronts had a little bit more tread life but I got rid of 'em anyways and put on Michelin Pilot All-Season (A/S) tires. I've got about 36,000 miles and change on 'em. They are starting to wear now but these have held strong for long hauls. :)