I've got a beefy case for my phone on the back of which I stuck a Garmin-mounting carbuncle—I use this case specifically for cycling. I've got a generic Garmin mount on the bike. So far so good. I mostly ride with the screen off and audio notifications on, using either Ride with GPS or Cyclemeter, depending on whether I need navigation cues or not (sometimes I even use both at the same time). RwGPS is remarkably battery-efficient. Cyclemeter is less so, but I still find that I've got at least 50% charge left after a 6-hour ride using it.