I don't use my Galaxy S3 for my GPS on the bike, but I have used it when traveling around France, mostly walking. With the GPS the phone eats up battery amazingly fast. The obvious effect of this is the phone gets pretty warm. Not burn-your-hand warm, but "this-can't-be-good" warm. I also have had "CoPilot GPS" it lock up using it on my Samsung and y iPad mini. In fact, I couldn't get this app to work on my iPad mini until I suppressed POI display. Even then it often complained on startup. There's no point in my using it for GPS on the bike since I have the long-ago sunk cost of my Zumo 660, which always works. This thing mediates calls from my Samsung and works OK.
Yeah, bluetooth is generally a headache. My Sena headset highly reliably connects to my Zumo, but the Samsung often needs coaxing to connect to the Zumo. It'll work fine for weeks then I have to perform a manual reconnect on restart of the Zumo for some number of times, then it works fine again for weeks. The Samsung almost always hooks right up to my Prius bluetooth just fine, though. Go figure.
I don't generally listen to music while riding. There are numerous reasons for this. Foremost is that I like to listen to whole operas. I have yet to find a music player that handles this situation well. One has to concoct playlists consisting of the proper sequencing of multiple CDs and each and every device type does it differently and some resist the desire to simply play through an opera in proper sequence once and stop. I'd also like to be able to do this and set up what I would call a temporary set of "queued playlists" so that when I'm on the road it would play through a couple of operas in sequence and thereby last me between fuel stops. Then there's the fidelity problem. And the trickiness of operating music controls while driving.