My Ruffy Tuffy tires (by Panaracer and Rivendell) have well over 6000 miles on them, and they seem like new. Never had a flat. Rode them from Butte, MT to Alaska in the summer of 2012. That was their first 3120 miles. Some of those roads were pretty rough, but never a flat.
I left the tires on for the 10 months after that, and added another 3-4000 miles. The only reason I took them off was because in August, 2013, I was beginning a tour around lakes Erie and Ontario, and I figured the tour leader would have a fit if he thought I was starting off the ride on 6000-mi tires. But I did not throw them away.
Recently, the new tires I put on 14 months ago wore out, and I decided to put back on my Ruffy Tuffys. I swear they look perfectly fine. I just did the 103-mi Pumpkin ride last Saturday on them too. Sure, they may weigh a little bit high (~300 g), but that is a small weight-price to pay for not having to change flats and even tires for years on end.
I rode just 35 miles today because I’ve been spending so much time “advertising” my new book. Check it out if you haven’t already: http://www.sunburypressstore.com/Head-Over-Wheels-9781620064986.htm