It does have its quirks, it can't be blindly trusted. A few years ago it was useless for many directions in my city, due to four facts:
- for two or so years it kept directing me through one road, which was permanently closed due to construction work. Yet, it was absolutely convinced that another road was closed all this time (due to the same construction work) - it wasn't, they put some temporary tarmac through the middle.
- yes, there's hardly any traffic on this brigde - perhaps because it's mass transport-only, closed to private cars? But yes, technicly the bridge isn't "closed", just closed to me.
- no, it is not faster to take the highway if it doesn't exist yet! (it was finished 3 or 4 years later, as planned; this made GPS useless for SO many trips...)
- no, I'm not flying over the river, there's a new bridge here...
Ok, that last one was just a case of old maps, easily fixed. But the one before - WTF?!?
In short - one function I want on a GPS is the ability to mark a place on the map, or a section of the road, and say "never direct me through this place, period", or "avoid this place for this trip only". No, the "alternative route" button does not work, because it has no idea why I want a different solution. It assumes that the road is blocked for some reason and tries to get you around that and back on the original route ASAP, which is useless if half of that route is in fact closed.