Just saw this vid showing how Twixtor can modify a 60fps movie into 1000fps, obviously not as good as the genuine article but its still pretty impressive. [ame="http://vimeo.com/13557939"]7D 1000 fps on Vimeo[/ame]
Adobe AF Pixel tweening does this. I did a test on a film once with a car travelling at 150mph past the camera - it didn't do too badly although it needed some post work.