Bluetooth skip not working
I had the same issue when trying to stream music over a Bluetooth connection from my iPhone to the stereo in my 2007 BMW. Worked fine with iOS 6, was broken after upgrading to iOS 7.

This issue can be fixed by disabling Control Center access from the lock screen: Go to Settings -> Control Center -> Access on Lock Screen; set this option to off.

(You will still be able to access Control Center after you unlock your phone, but not from the lock screen.)

Now I'm able to skip songs using both the buttons on the steering wheel and the ones on the stereo/nav unit again!