After upgrading to a MacBook Pro, I discovered that my Calculate Size Contextual Menu item (which calculated total size of everything selected in finder) wasn't showing up, even though it was installed. After digging around for a few days, I made my first real AppleScript -- a substitute for the non-functional CM item.
I added the script to Butler's smart items with a trigger hotkey, and it works just fine. (I still haven't figured out why when added to OnMyCommand items it shows the alert more times than necessary). Hope this helps somebody.
[robg adds: This worked for me on my MacBook, also via a Butler Smart Item.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060608030023113