I used the Maps app through much of the beta and never had any problems. I used it to drive from Orange County to San Diego and Los Angeles several times. It didn't route me any different than my prior driving app, Motion X.
In truth, I just don't think I'm much of a Maps power user. I put in an address and I go there. I don't do much more and, as a result, didn't bump into a lot of Maps' sins. I'm not denying that the app has troubles. It does.
My biggest gripe with the Maps app is driving at night. It displays the driving directions in the full screen with a brightly colored background. I use a window mount and the Maps app plays hell on my night vision. It feels like a safety hazard for me and I stopped using it when driving at night. I complained about this on a recent MPU episode and listener Mike wrote in with a great temporary fix.
Go in the Settings app and tap on the Accessibility screen. Then tap the Triple-click Home button and select Invert Colors. Now tripple tapping the home screen inverts your iPhone colors, which makes the maps nice and dark at night. I recognize this isn't a long term solution and Apple should fix this properly but for now, it works.