I've recently replaced my 2011 MacBook Air with a brand new MacBook Pro. That makes me a professional. I was looking forward to less of the spinning wheel but, in fact, am getting it just as much. Especially when working with PDFs in Preview. Zooming in and out of them, panning around them etc. makes the computer freeze for several seconds, lag, go choppy and then start spinning its little wheel. Why? What's so tricky about a black and white, line-drawn PDF?