I like it for mapping out routes in areas that I know. I can then drag the line to my prefered route where necessary. I can tell that they keep updating it.
After my Sunday ride, where my computer stopped working at mile 33, I used Google Maps to estimate my total mileage. I was really surprised when the route that Google gave me would have included about 2 miles on a root-filled, sometimes-muddy dirt hiking trail. I ride the trail on my CX and mountain bike, but there are easy roads to get from points A to B without using this dirt trail. It's things like that that would make me think twice before using Google Maps as my sole source for biking routes in areas that I don't know.