There are several new features of note introduced in version 1.4. First is the iGlasses Manager. It allows you to switch iGlasses on and off on a per-application basis, so you can use the filters in, say, iChat, but not in iMovie. Second, you can now use iGlasses in many more applications. Version 1.4 includes support for Comic Life, Delicious Library, Camfrog, jmeeting, WebcamTweaker, CamSpinner, Funny Photographer, CamGrabber, and more. Finally, 1.4 introduces enhanced AppleScript scriptability. I'm sure you can use the scriptability for some sort of twisted April Fool's prank, but I'm unsure as to what else it might be helpful for.
You can buy a copy of iGlasses for $8 at the ecamm website, which isn't a huge amount of money, but be aware that a lot of this same functionality looks like it will be built into Leopard's iChat when it bows later this year.