Got my One two days ago and for two days I couldn't get it to mass storage, using the USB wire that came with it. Then I noticed a tiny amount of wiggle inside the phones USB connection. So then I GENTLY lifted the USB wire UP as I kept the phone flat, voila, my Windows 7 laptop gave its customary 'ba-ding' and I was in business!
Guess the USB tolerances inside my One are a bit out. Hope this helps you guys :-)