Please keep scrolling
There is still a bit of a debate as whether there is a 'fold' on a web page. Will the user scroll to find more content or just look at what's in front of them?
Nike Better World and Campaign Monitor replicate the concept of site pages with sections of the vertical page. You can scroll down to each individual content section and see the images animate vertically at different rates creating a parallax scrolling effect. This creates a wonderful feeling of motion, making it a pleasure to explore the content, although scrolling with the scroll wheel can make it rather jumpy - it's best viewed by clicking the navigation buttons.
Telling a story
On Ben the Bodyguard you are given a 'Scroll' call to action, then as you scroll down the page a story is revealed which eventually leads you to a call to action to provide your email address for updates. The story concept quickly draws you in, finally capturing your interest and making you eager to find out more.
Row to the pole uses a layered background effect, again using parallax scrolling, to make a more visually appealing page background. Using different scrolling rates for the page content, clouds and icebergs give a very lovely feeling of looking down at the page from the sky.
The scrolling effects on these examples easily enhance and enrich the user experience. Using an effect like this has to have a specific purpose though otherwise it could become a barrier to exploring the content within a site, rather than being an incentive to do so.