We're liking this idea. Even the cheapest clamshell phones these days have a secondary external display. Doesn't it make sense for your laptop as well?
ASUSTeK thinks it's a good idea. Their WSFe is the first production laptop to market with an secondary display, on the back of the primary LCD. You can use it to check your email (read only), reference notes to yourself, or (the best app) check for WiFi hotspots without having to open and wake up the laptop. Even better, they claim it can run for “hundreds of hours” on the charge of your laptop's battery. We don't buy that.
There've been rumors of Apple building a WiFi detector, like the one on your keychain, into its next line of MacBooks. This takes the idea one step farther.
ASUS WSFe Dual-Screen Laptop [Tech Blog]