I had no problems with two droid Xs and a galaxy nexus, but a friend of mine had a nexus and couldn't get a reliable GPS signal to save his life. Are you using the stock ROM on the phone?

I use a garmin 500 now, which is a superior solution IMO because you are much more likely to have your phone available in case you get lost or need to make a call. The battery also lasts a lot longer. As for turn by turn, when I do a long ride over unfamiliar roads, I'll load it in - it's usually great at telling me I just missed a turn, but it's better than getting completely lost. You can tell when you have a turn coming up, which is a plus, but it's not the fastest reacting computer.