Apple Mail 6.2 doesn't download messages from Gmail over POP3

I'm trying to set up my POP3 Gmail account on a Retina MBP running OS X 10.8.2. A few months ago, I managed to do the same thing, the first time around, on an iMac, working with the same Gmail account and under an earlier Mountain Lion release. This time, Mail gives me no errors, and despite having followed Google's guidelines on how to set up POP3 email on Apple Mail, no messages will download on the MBP, even after checking for new mail, and right-clicking the account to force download. Has anyone encountered this issue, and found a fix?