I'm on Xbox No4 and to be honest I've not had a problem with customer service. A quick phonecall and they Email me a shipping label, bang it in a box and a week or so later a new box comes in the post. This one has lasted over a year so I think its not a problem machine like the first three were. The only real pain for me is re-downloading all the stuff Ive bought on live in the past five years.
I know they shouldn't go wrong but they sort the problem without question and issue a new warranty so you should never be out of pocket but it is an inconvinience.
It wont stop me buying the next machine they bring out, I'd rather have a ticking time bomb than a gaystation