I got a 2nd hand Biologic one a few years ago on eBay to use with a 3GS. Worked well, was secure and waterproof (used it in the rain many times). At the time they were silly money new, and not a lot of choice either, but there are a lot more options now and prices have come down.
I’d use it just for mapping really, I’m new to the area and use bike hike to make routes but can’t remember all of the turns and don’t have a printer. Its for using on my road bike so having to stop and fish out my phone to look where the turn is gets annoying.
Used the Topeak Ridecase on two bikes since April last year – one has the stem cap mount, the other the handlebar mount. No issues (although only one “off”) and iPhone has stayed attached and undamaged. Rubberised cover has kept the phone dry. Should I ever get an iPhone 5, I’ll be buying the case for it and gaining a mount for bike #3.