If you take care of your Frontier, it will take care of you. I am a Nissan Technician and I see alot of vehicles everyday need trannys or engines or whatnot because people dont take care of them like they should. Change the oil every 3K miles and rotate the tires every 7500 miles. Make sure to get your regular major maintinence @ 30K, 60K, 90K, etc.
I have a 2008 Frontier 2wd 4cyl SE King Cag with 6,100 miles on it. I have a 100,000 mile warranty. The only problem I have had is I had to replace the high side A/C tube b/c of a freon leak. Anyway, if you do regular maintainence when it is due, and dont drive it like a racecar, it will give you many years of dependable service. For example, we have a 2003 Nissan Frontier on our lot that belonged to a good customer and he traded it in on an 09 Frontier and his 2003 had 650,000 miles on it and it was all original.