I can only speak of Google Maps on Android of course. Back in the days of Gingerbread on my Desire I'm pretty darn sure the voice navigation was a lot more reliable. These days on my Galaxy SIII JB I noticed the following:
1. The warning ahead of turns are at times not present, or inaccurate. Most of the time the inaccuracy are late warnings, i.e. I am already in the turn by the time it says "Turn left now". Warning ahead is also variable, at times missing.
2. Roundabouts! This is the worst by far. At times it is absolutely silent - I have to glance at the screen to see which exit I'm supposed to take. At other times it will say incorrect things, e.g. "Exit the roundabout" just as I'm entering the roundabout with the screen instructing me to take the 3rd exit.
I wondered if there's something dodgy about my GPS hardware so I bought CoPilot and it works like a charm!
Anyone else noticed this?