The ever-watchful NeoGAF has stumbled across evidence that Steam may be adding the ability to lend your games to other players. Can you imagine? User Grief.exe found the following lines in the steamui_english file:
Find this for yourself by updating to Steam Beta and going to Steam > Settings > Beta Participation and then looking for the aforementioned file in the /Steam/Public folder.
Such a feature sure would be nice. I'd no longer need to do the "offline" trick to let my sister check out my library.