I've been bugging them for almost two years now - and they've finally done it.
And they've done it right, too; with a bitcoin address on their donations pages, right under the usual fiat/CC/PayPal stuff:
http://www.linuxmint.com/donors.phpI know a lot of us use Mint, and they're (at the moment) the most successful linux distro out there - they surpassed Ubuntu some time ago (check DisttroWatch).
Let's show them some love...