I've been trying out Waze for the last week. I find that I like it a lot. I run it alongside my Garmin 1690 GPS (latest map updates) and find that Waze can sometimes route better than my Garmin.
I'm still getting used to Waze, but so far, I like it. It seems to know road changes quicker than the latest mapset from Garmin... by a wide margin. Garmin is often months behind in road changes... just the nature of the beast.