There are a few things I have witnessed becoming obsolete in the past few years, the first being autographs. I haven’t been asked for an autograph since the invention of the iPhone with a front-facing camera. The only memento ‘kids these days’ want is a selfie. It’s part of the new currency, which seems to be ‘how many followers you have on Instagram.’
I’d say it’s probably 70/30 on iDevices vs. MacBook. Most of the MacBook Air time is work-related. And that figure is so heavily tilted in the iDevices favor because I use the iPhone far more than any other device.
That said, when it comes to “general computing”, I much prefer to use the iPad Air (with the Logitech keyboard) for almost everything. But I suspect a rumored 12” Retina MacBook Air could tilt the numbers back in the MacBook favor, if only temporarily.