I'm helping out on a site that uses Google maps at the moment, and so far it has been reasonably accurate, the only problem is that sometimes when you're plotting a location it always comes out with the marker a little too far north, so you have to re-plot it again to get it right.
I checked on some new developments locally, and it looks like Google are up to date in my area up to about a year ago - most of the new properties are listed.