You're in a hotel room, and you want to hook up to the in-room Wi-Fi. And guess what? It sucks, just like at every other hotel you ever stayed at. So Instead you dig out your MacBook and hook it up to the hotel's Ethernet cable, and use internet sharing to generate your own wireless network.
Wait… The newest MacBooks Air don't have Ethernet ports. But don't worry: you can pick up the $60 mySpot from Kanex, a little dongle which takes an Ethernet connector and turns its sweet network payload into a wireless cloud, ready for all your iDevices and your non-Ethernet MacBook Air.