In the MacMini, MacBook and MacBook Air it might be good, but not for the MacBook Pro lineup. And not for the iMac or Mac Pro either, at least not in the near future. Plus I think we need to see what it's capable of in terms of performace before it finds it's way into the stationary computers.
I'm all for more competition in the CPU industry. Note only will it stoke the fires AMD keeps alive under Intel's feet, it will enhance R&D and lower prices for us all. And that's a good thing. ARM seems better positioned right now for the handheld computer market (smart phones and tablets) but Intel knows that is where computing is going. So the next few years will be interesting to watch.
Why? Because ARM CPUs are a proven product. There's no reason Apple could not use ARM here and Intel there - just as Dell or Gigabyte use AMD here and Intel there. Or Apple could get back in bed with Motorola too.