If you use the ⌘I shortcut in finder with a file selected you get a ‘Get Info’ window. If you do this with 20 files selected you get 20 windows, In Snow Leopard if 10 or more file were selected you got a Summary window. I found this handy for getting the disk usage for a bunch of files.

If you would like to change it to always get the Summary window, which I find useful in case of selecting all in a folder and accidentally hitting ⌘I you do not a have many many windows to close.

Open System preferences, select keyboard.

Keyboard Shortcuts -> Application Shortcut -> +

Application, select Finder.
Menu Title, enter ‘Summary Get Info’
Keyboard Shortcut, press ⌘I