According to a story in the Daily Princetonian, 45% of computers purchased through the university were Macs this year. In 2003, only 15% of incoming freshmen bought Macs. In 2004, that went up to 25%, and last year it was 38%. (Figures include only computers purchased through the university.)
Students in the article cite PC problems due to spyware and viruses as a key factor in their decision to go with a Mac. Now that the market share for Mac is going up, though, I bet the malware will increase too.