I was looking to purchase an app a couple months ago and was strongly considering co-pilot, but just could not justify it because:

- Cost got close to the point if I wanted the features of a stand alone GPS.
- My Nexus One is a power hog, especially with GPS and screen on full time. It will drain the battery even if plugged into the car. Add in bluetooth, music etc. and it is even worse.
- Hassle of trying to use the phone as a phone and GPS at the same time.
- Murphy's law says an app will crash at the worst time, which probably means on a complicated routing in dangerous traffic.
- Slow satellite lock if you are off the cell phone grid.

I ended up going with a new Garmin unit with lifetime maps. More expensive, but it is the better functional option. I'll still rely on Google maps for a quick navigation to a restaurant or something I just found, but for long trips the Nuvi wins.