"Animoto is an excellent tool for creating audio slideshows. But there are some limitations to it that some teachers don't like. Most notable of those limitations is the time limit (30 seconds unless you get an Animoto for Education account), lack of space for text, and that students have to remember a username and password to use it. The YouTube slideshow tool provides a tool for creating audio slideshows without those three limitations of Animoto."
Via Beth Dichter, Seth Dixon