TUAW just featured an app called DropCopy yesterday. It has been around for about 4 years and one of the first sentences I read popped out and reminded me of this question.
For one, DropCopy can auto-accept file transfers. Meaning, your recipient needn't be in front of his/her machine to initiate or accept a transfer. That's handy if you want some files to be waiting at a remote work station upon your arrival.
It's a bit of give-and-take. DropCopy DOES require all the computers to be on the same network. It does not set up a second channel AdHoc network even where supported, but it offers compatibility outside of Lion and lots of additional features.
The way it works is similar to AirDrop. Just drag-and-drop your file onto the Dropzone and it'll show all the possible destinations. Participating machines must be running DropCopy on the same network. Simple.
Via TUAW's screenshot, DropCopy can also transfer your clipboard contents, send text messages, and also supports multiple computers.
DropCopy is free for the first 3 computers, can be downloaded for free on the Mac App Store, purchased from 10base-t interactive's website, and even has an iOS version.