We had one that had worked fine for about four years. We had very hard water, and no filtration. Like anything else, it required cleaning and maintenance, which were both neglected for the most part. Before it went south on us, about the only issue was that the injector needle would get plugged from time to time.
We have a newer model that's about a year old, and soft water in our new home. This model has a "Rinse" cycle that simply runs hot water and steam for a few seconds to keep the injector needle clean. So far, no problems.
One of the guys at my old workplace had one at his desk that he allowed everyone to use. When it crapped out within a year, he called Keurig about it and they replaced it with a new model at no cost. I'd call that pretty good customer service.