As far as I can tell, the only new feature in FastScripts 2.4 is a software update mechanism. But – hey! – gotta be up-to-date, right? Daniel Jalkut, the author, has also killed off FastScripts Lite; the full version is now capable of running in “Lite” mode.
If you run any sort of scripts regularly, it’s a must-have. (Here’s the full feature list.)