When spelunking the file system with QuickSilver, you can use the "/" key to navigate one level down on a folder and "SHIFT-/" to back up a folder. The combination of this with smart incremental search for names makes QuickSilver more efficient than most Finder operations.
One other file/folder related trick. If you want to select all the files in a folder, navigate into the folder and hit "APPLE -A". This is the standard "select all" keyboard shortcut, but it took me a little while to realize this worked in QuickSilver too.
QuickSilver: let go