We have used Google Maps in our travels for years, and it is usually quite accurate. We have found glitches, but nothing serious.
Yesterday, I was fooling around on the net, and pulled up directions from Brenham, Texas to our house.
Google offered three alternative routes, including Hwy 105 through Conroe (the shortest miles/longest drive time) and US 290 to Beltway 8 (the way we normally go) but the one recommended was US 290 to Texas 99 - the new Grand Parkway that will eventually circle Houston. Their directions read, in part:
Merge onto US-290 E
Take the exit toward TX-99
Keep left at the fork and merge onto TX-99
Partial toll road
Continue on Valley Ranch Pkwy. Take Eastex Freeway Service Rd and FM 1485 E to Conners Rd in Harris County
28 min (16.1 mi)