We've bounced all sorts of software applications round our computers in the past, but this one has possibly had the most substantial impact.
Designed for stop-frame animation (take a series of pictures quite similar, string them together, add audio etc), it enables such films to be put together in a straightforward and accessible way. My son (software-tester-in-chief), who had previously done a little animation of a model dalek with Windows MovieMaker and an add-on, animated some chocolate cars (the fruit of which can be seen at [...]). It takes patience and dedication - this constituted a couple of hours work - but is pretty effective.
However, having opened the can of worms that is video editing and production, my son rapidly became more absorbed by other possibilities, which led to the purchase of more general video editing software and may well lead to buying a new video camera, (or one that is more useful than the old DV one) and constructing new greenscreen equipment ... and doubtless to more YouTube videos.
This software is still particularly well-suited to producing animations, and would most likely continue to be used for this, even with more sophisticated general software. It's a very good starting place for somebody dipping their toes into the field of video creation.