I don't mean to throw off the curve here... but I'm on my 9th 360 since launch. Well, technically, 8th and 9th.
My launch system lasted until May of '06, red-ringed and was quickly replaced. The next one died in October. Two weeks later, I get a refurb from Microsoft that had been through a fire in the UPS truck, but still magically worked... until the fall update bricked it. Two weeks after that, I get a refurb with a bad GPU out of the box. Sent that one back in and Microsoft lost my return... for two months, during which time I bought a Core system so I could play Gears, CoD3, and R6:Vegas. 4 weeks after buying the Core, it red-ringed, so I returned it to Circuit City and got another one. January of '07, Microsoft finally sent me a working Premium back (three months to the day of originally sending my system in). Then in May or June, that system red-ringed, so I pulled the Core back out of the closet (which I kept for a spare) until I got my Premium back.
So numbers 8 and 9 are what I'm on now. My 360 is set up in my home theater, which stays at 74 degrees year round. It has 6" of space in every direction, is not in an entertainment center, sits on a hard flat surface, is not hooked to a surge protector (since MS claims that kills them), and I've had the dedicated circuit for the room checked by an electrician.
Oddly enough, I'm not bitching. I mean, yeah it sucks that for the first time in my gaming history, I had to buy a second machine as a backup because of how unreliable they are. But all that aside, the 360 is fun as hell. Let's just hope they iron out all these issues with the new 65nm Falcon chipset so people can concentrate more on the gaming and less on the eventual RROD.