AirDrop is a new feature in OS X Lion that lets you wirelessly send files to other OS X Lion users, without Wi-Fi. But it only works on certain Macs. Apple has posted a KnowledgeBase article explaining which ones work:
Macs that support AirDrop in OS X Lion The following list shows the earliest of each Mac model type that is supported. If your Mac is the same, or newer than the model listed, then it supports AirDrop.
- MacBookPro (Late 2008 or newer)
- MacBook Air (Late 2010 or newer)
- MacBook (Late 2008 or newer)
- iMac (Early 2009 or newer)
- Mac Mini (Mid 2010 or newer)
- Mac Pro (Early 2009 with AirPort Extreme card, or Mid 2010)