I've found it perfectly acceptable in various parts of Germany, Belgium, France and the Netherlands. I'm currently in Amsterdam and (so far) it's very good indeed.

Map retrieval can be slow on trains travelling at high speeds, as wco81 says, but that's obviously a fairly demanding use (and typically not essential: train drivers tend not to need your help finding their way ). It is certainly almost always good enough for driving, walking or using local public transport (to find the nearest bus or tram stop, for example, or to check that your taxi driver is taking a sensible route).