Yup, I use Nike+ Running and Slacker Radio, and like having the added safety of GPS and being able to make an emergency call. I gave up on armbands a while back and now swear by my Flipbelt, which keeps the phone tight against the small of my back. Jaybird BluebudsX wireless IEMs complete my setup.
It will be nice to have run controls (and hopefully music controls if/when Slacker updates their app) without having to pull the phone out, which is a bit of a pain.
That said, if/when Apple allows the Nike app to access the HR sensor, and if the upcoming Apple Beats subscription service is good and allows playlist downloads to the Watch, I could
totally see going phone-less for shorter, harder training runs where GPS is irrelevant because it's the same route every time, and you're never too far from home so the ability to "call for backup" would be less important.
Bonus: Pay for a frappucino and lemon bar using Passbook or Apple Pay after run, and pile those calories right back on.

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Can you run the native Workout app (HR and data completeness) and Nike+ Running (coaching, leaderboards, voice feedback) at the same time?