Applescript (or other Quicksilver accessible thing) for hibernating a snow leopard mac?
You can use Deep Sleep. It's a Dashboard widget that will put your mac into hibernation mode.

Edit: from the website


  Deep Sleep can also be used as a command line utility


From there, you can check out if QuickSilver can launch command line programs.
You can also package it in a .app -for example using Automator- and launch it with QuickSilver.

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Careful, be aware there's 2 sleep mode.

The normal one you can trigger using ⌥+⌘+Eject

And the hibernate (or Safe Sleep) mode.

You can read about the differences between them here.