My android phone (Droid 1) seems to be as accurate as my stand alone GPS (Garmin eTrex legend HCx), its not as sensitive though, dark clouds, trees, buildings will block the signal. It will take longer to get a fix sometimes a few minutes if a cloudy day and can't get a fix at all inside my office building where my Garmin gets a fix in a few seconds and can even get a fix inside buildings.
The Garmin has better battery life, a pair of AA eneloops or lithium can run 18-20 hours where the android phone can maybe run 12 if you don't do too much else but use the GPS.
The phones display is bigger and nicer but is a backlit like a laptop so it washes out in bright sun where the Garmin is a reflective display like a watch so the brighter the sunlight the easier it is to read.