Debuting with the Winter 2012 Steam Sale is something called "wishlist notifications" which appears to be:
We'll let you know by email or through our mobile app when the games on your Wishlist are on sale as a Daily Deal, Midweek Madness or Weekend Deal. Whether you're riding the bus, walking the dog, or stuck in a meeting, you'll know when there's a deal!
I haven't got a mobile device capable of using the Steam mobile app, so I'm limited to email-based notifications. How do I set up or configure email notifications for my wishlist items?