I know the Tire Rack sponsors this section of the Forum but...
So I had this same issue. I replaced my suspension with BMW OEM components at 183,000 miles last June. Did my FIRST alignment at that mileage. I routinely averaged about 35,000 miles per set of tires, which is on my sport package 325i with a square set up - switched to 18" CSLs - running 235/40-18 ultra high performance all-season. Well the shop totally effed the alignment (toe was way out) and I went through the rear tires really quick (they had about 17K on them at the time of the alignment and only went another 10K) I replaced the tires in November 2011. Rotated them in December at 5,000 miles. In February I went to rotate them again at 11,000 total miles on the new set and the rears were toast. I was pissed. Went back to alignment shop and of course they said the alignment was in spec, but they could "tweak it" to make it better. BS BS BS...
Long story short, called tire rack. Good luck with mileage warranty. Since I have my own shop at home, I buy tires from the Rack, ship to my house, remove the wheels, take everything to a tire shop in my pickup and have the tires mounted on the rims and I reinstall everything back home - so my car never goes to the shop to get tires installed, thus no record of mileage when the tires are installed. Now I have records of every fill up by date, so I can prove the date I have the tires installed, and inference to the mileage they were installed (by me), but that was no help.
To make a warranty claim at the Rack, you have to ship the tires back to them, which costs you money. In my case the issue was obviously the alignment, so the Rack gets to point at the alignment shop and the alignment shop gets to point at the tires (i.e. leave it to a mileage claim with the Rack). So I was SOL.
Lesson learned. My advice is just get tires from a reputable tire shop and have the alignment checked and set properly. If you then find your tires do not last to the warranty mileage, you can go back to the shop that sold you the tires and did the alignment and not have any finger pointing. The Rack doesn't save you enough money to make it worth giving up convenient claim to a treadwear warranty.