The retreads from treadwright actually do fairly well. That is, if they are on your DD, NOT your trail rig. The can go through mud holes and such with no problems. However, it is indeed when people start to air down and rock crawl that they fail on the trail. I have known MANY people to put 20,000 street miles on retreads with no problems at all. But I've also seen people take them out their first day, lower the psi, crawl, and rip the tread off.
Pepatt said the tires laying on the side of the road are brand new. I must disagree. These tires do come from the 18-wheelers. Where your wrong is I dont know a single trucking company that buys NEW tires. In todays world, its all about maximizing profit and in order to do this they have to keep purchase prices to a minumum. Why would they pay twice the price for new if they can get retreads? Plus they order in bulk so they get discounts.
Personal opinion--If its your daily driver buy them, they are worth the money. If its your trail rig, you're better off buying brand new, more expensive, name brand tires. Honestly, best bang for your buck is a Kelly Safari DTR. They arent exactly cheap but they are unstoppable on any terrain. They dont have the highest ratings and are noisy on the highway but you wont get stuck anywhere. They are HIGHLY under rated. Mud, snow, slush, rain, anything, just hit the gas and go. I've had great success with DTR's and recommend them to anyone.
Good example: my buddy has a driveway that is about a 40* angle and was covered in 8" of snow this past winter. His DTRs were about half worn but he didnt even have to lock in the 4x4 to get up the driveway. I have seen several people slip and slide all up and down his driveway in 4x4 in the winter. I myself had to lock in with snow tires. I am sorry to say, I was driving a J**P. However, I wont knock the j**ps capabilities because as far as winter goes, I've never gotten stuck or slid half way through an intersection. Its too "pretty" to ever see a trail though.
Edit: Treadwrights biggest problem is they almost always have to back order things. Mostly the bigger tires but they do tend to run out of the smaller ones too.