One of the most futurey features of Lion is the ability to share files between Macs with no Internet connection. Right now, sharing files is often very tricky--two Macs on the same network can manage it relatively easily, but away from a network? Forget it, it's time to break out the thumb drives. Enter AirDrop.
Combining Bluetooth accessibility and Wi-Fi speed, AirDrop connects through a peer-to-peer Wi-Fi connection that requires no base station. Macs running Lion can drag and drop files to each other as long as they’re within 30 feet, and the app isn’t even obstructed when both computers do happen to be connected to two different Wi-Fi base stations. Best of all, it's ridiculously easy to use: Lion automatically finds other AirDrop-compatible computers (basically, a Mac running Lion) nearby, and lists them in the Finder. Then you just drag-and-drop any files you want to that lucky neighbor's name.
The files are encrypted to prevent hacking, and Apple actually creates a firewall to protect you and the person with whom you're sharing while using AirDrop. Plus, you can make yourself invisible very easily: Just close the Finder window, or click outside the AirDrop window to focus elsewhere. Done!