Instant send feature in quicksilver
There are several ways to use the currently selected thing (files/folders in finder, selected text in other applications, ...) in Quicksilver.

There is the ⌘⎋ (command-escape) shortcut. It opens the Quicksilver interface with the selected thing in the first pane

Or you can open the Quicksilver interface and use the "Current Selection" proxy object. That does the same thing as above, but when the interface is already active. For that, you need to activate "Enable advanced features" in Preferences -> Application.

Using the "Current Selection" proxy object, you can also make your own triggers that use the thing that's selected at the time you use the trigger. Check out the Quicksilver Manual somewhere around page 38 for more information on that.