I had a $399 Pro that was manufactured in October of 2005 that I bought in Feb of 2006, it lasted for 3 years, no problems. It stopped displaying video, not sure why, no picture whatsoever would show up (tested it on multiple TV's with multiple Video cables, VGA, SD, HD), nothing worked. The repair was $100, so I decided to buy an Arcade from Circuit City for $120 during their going out of business sale. Definitely the wiser decision, new controller, memory card, that Arcade disc and a late 2008 manufactured console for 40% cheaper. I just popped my hard drive on and everything has worked out fine so far.
I still have the broken console in the Arcade box, not sure what to do with it, maybe when I get so money I'll have it repaired.
Overall, I'd say I'm one of the fortunate 360 owners in terms of hardware reliability.