Dear Aunt TUAW,
I want to use AirDrop between my older iMac and my new MacBook Air. How can I do this? They're both running Lion but AirDrop is only enabled on the MBA.
Your loving nephew,
You can enable AirDrop for many older Lion systems at the Terminal command line. Enter:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1
After setting the defaults, you'll need to restart Finder:
Once you do, you should be able to use AirDrop on your local Wi-Fi network. Auntie is currently using AirDrop from her early 2009 Mac mini without any trouble.