@Liutke, the example projects that come with Spine have a license that allows derivative works to be made (such as portfolio animations!) as long as they're not used for commercial purposes (such as reselling the assets) so you should be good!
Moreover, you can find several additional projects to animate that are downloadable here: Spine: Twitch
(If you do animate them, I'd love to see the result!)
A couple of nice examples:
Michael Jackson Spine
Riding a dinosaur with Kinect
