I've just recently gotten the Wahoo/iPhone combo on my bike. For comparison, I'm coming to Ant+ having been a Polar user - I love the fact that a single small Ant+ sensor by my pedal can pull both speed and cadence off the back wheel (good for being on a trainer), is replacing two larger Polar sensors, and has longer range.
I'm pulling the signals into an iPhone 4S using the wahoo case and handlebar mount. I run with the phone in the same case in a back pocket. Battery life isn't fantastic (3 hours or so - prob more with wifi off - wish there was a way to kill all the radios but the gps) but there's an expansion battery pack you can get, and I like jpr95's suggestion - might have to try that for centurys, etc.
The part where this combo shines: throw on a set of bluetooth headphones. Now you have music for motivation. Many of the fitness apps (I'm using MapMyFitness+, but I've also used and like Cyclemeter) can be set to reduce volume on the music and report stats to you verbally on triggers like distance, time, volume button press, etc. If like me you're someone who is motivated to work out by tracking what you've done, you can't ask for more than what many apps do - maps, cadence, heart rate info, distance - all kept on the bike and online. Use the screen to look back at previous workouts, share ridemaps with others, compete against your own previous times, etc.
Kinda great, especially considering I normally would ride with the phone on me for emergencies anyway. So basically I've gained loads of functionality while removing two older and larger sensors and a watch from the bike.
The cons: Battery life could be longer. The iphone is a big thing to have mounted on the handlebars, no arguing that (I'm considering an ant+ computer like the Node 1 to supplement the phone and move the phone to the jersey pocket.)
Also for what its worth, a friend I've ridden with has a similar setup with an android phone, and he's able to disable all radios except the GPS, which would extend battery life quite a bit. (And you may be able to do that after rooting the iphone, but that's not an option for me.)
Keep the rubber side down,
-Tim