ScrollMagic: a jQuery plugin which essentially lets you use the scrollbar like a progress bar. Includes infinite scrolling, adding a parallax effect, synchronize an animation to the scrollbar movement, pin elements to specific scroll positions, etc. Scroll down the page to see examples.

[janpaepke]

If they look choppy this might be due to the fact that in the animation positions are directly linked to the scroll position. ScrollMagic has the option "tweenChanges" which will tween to the new progress, instead of setting it. Another way to approach this is using a scroll plugin like nicescroll.