Some of them link to http://dynamicdrive.com/ , which is probably where Chruser / Wetwired got the script (looks like Chruser's handiwork, though)
I think it has something to do with the whole April 1st thing.. but maybe not. It IS messing around with my browser though, when they go offscreen it puts a horizontal scrollbar at the bottom (for obvious reasons), when they come back the scrollbar goes away (as you would expect). So I get a flashing scrollbar.
If it slows your computer down then I guess it isn't as good of a thing as I thought. I am at college now at the library and this doesn't slow it down at all. My computer at home is crappy so it probably will be slowed down.