I got my 360 elite in 2007 and it only failed the day Mass Effect 2 came out (Crashed during gameplay) and due to the error being an E74 error I had it fixed for free and no problems since.
So in all I have had the 1st 360 I ever owned.
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Zero. I'm still on my first one after 4 years. However my Xbox One is already dying and will already need to be replaced soon...