I never use the GPS without reviewing the route first. Anyone that blindly follows a GPS pretty much deserves what they get. It usually takes about 10 minutes to check a route, so you're not surprised by what comes along. This is done on a computer using either Google Earth/Maps or Basecamp.
I rarely look at it since that's one of the reasons I use it instead of maps: it tells me what exit, what street, and where to turn. But the thing is, the route has been vetted beforehand, by me, so I know that what it tells me to do is correct. Just assuming that it is going to tell you exactly where you need to go without pre-checking...well you know what they say about assume.