Yeah well if its worth the performance benefit then I will replace them every month (even though that sounds like quite an exageration since i have been running them for about three weeks now, hitting the dirt about three to four times a week and taking the kids out on paved roads while pulling a babytrailer, several times a week.) I have to deal with some rooty trails, where I ride. If you arent worried about the wear issues then they are definately worth your $. In the early 90s everybody griped about the Continental XC for the rear, because it did'nt wear well, but in thier day they were worth thier weight in gold from a performance standpoint.
you can also get the DTC version. last a long time, rolls much faster, and still corners great. basically its sticky on the sides and hard down the middle. i have been running one on the rear on my bike for about 1.5 years and its still going strong.