My nav like others who have posted fails intermittently. In other words, it does not work (not a map issue or a GPS tracking issue), it just freezes or won't set a destination or it displays a nav card fault. The annoying thing is that the nav does work about 85% of the time so it is not something I can take in and be sure that the problem will be repeated. Invariably, like the time I needed to take my son to a new doctor, the nav fails making me very frustrated, lost and late. My nav fails enough that I have taken to printing Google maps whenever I go somewhere unfamiliar (why did I pay for nav again)? Because of my generally poor sense of direction, I have gotten nav systems in my cars as soon as they were available. I have never had a nav system as bad as this (with respect to failures, some systems are more cumbersome or have worse UIs or even older maps, but once you figured out how they worked, they all worked).
I am hoping the big update with new maps fixes this because this level of failure is unacceptable in any production product.