Steam client beta adds remote install support
The latest version of Steam allows users to manage their library of games from any web browser.
As detailed on the Steam forums, the feature is in testing as of the latest beta client update.
You'll need to leave your Steam client running on your PC or Mac at home in order for remote management to work, but assuming you don't mind forking out for enormous power bills you can then log into Steam through your browser and make changes.
If the import of this addition hasn't hit you yet, you can buy games while you're out and about, and start them installing then and there - particularly good news for anticipated new releases which don't offer pre-loading.