Just got the 10.1.2 update so I could install the December 2001 Dev Tools just so I could play with AppleScript Studio.
Despite the unfortunate acronym, this thing is really cool. It's basically a plugin to the Project Builder/Interface Builder IDEs and allows you to create GUI-based AppleScript applications. In addition, you can mix Obj-C/Java code with AppleScript and since AppleScripts can also call *NIX shell scripts (at least in OS X) this becomes a very powerful tool, indeed.
So far, I've just played with the tutorial but this looks like it has tons of potential.