Apple is a publicly held corporation, they disclose sales to investors. Look at a chart through Q4 2009. Or the latest report, which indicated that they hit a quarterly record for Macs sold and a 33% increase year-on-year.
I'm not a Mac person (just iPods ), but I personally have seen several people I know switch, and Apples' sales numbers are qualitative data that backs up my assertion.
EDIT: Oh, and the majority of people who graduated in my high school macs proceeded to get MBPs. When I say a majority did, I mean more than half, and I think it would be safer to say 75%+. There's a reason why this picture exists
Yeah but how much bigger % are PC sales up year over year from 09-10? It might not be 33% but probably close. Fact is everyone is upgrading their computers in the last few months. Be more objective now. I just bought my Pavilion 2 months ago and Mini just a week ago. So that's 1 PC and 1 Mac in 2 different quarters from 1 customer!