I did not buy an extended warranty when I purchased my '05 V6 w/ 70k miles back in September of 2010. I drive almost 35k miles a year, so it just wasn't worth it for me. It's kind of a gamble buying any used vehicle, but I did make sure to check service history and common warranty items like the tcase actuator and such. The only thing that makes me nervous is that I doubt the engine was ever broken in correctly, and I doubt the first few oil changes were done at the recommended intervals. I've been reading a few threads about the V6 blowing up, and I'm scared! I am comfortable doing almost any work on my truck, except for an engine swap!
I also had a bunch of CELs come on within a week of having the truck... got the code read at AutoZone for free (small vapor leak), then tried reseating the gas cap and clearing the CEL by diconnecting the battery, but that didn't work. A new cap solved the problem though. Also, the Lexus dealership that I bought it from was very willing to make it right had the gas cap not done the trick. This at least gave me the confidence to drive the truck hard during the 60 day warranty period to potentially uncover any underlying issues.