Check out DONTCLICK.IT for a very cool concept site that shows an example of navigation without mouse clicks. One interesting implication is the biometric fingerprinting possibilities. One area of the site allows you to see the movements of previous visitors to the site. It seems possible to us that tracking the movements of a mouse, particularly when coupled with other behavior like server logs and navigation, will give an accurate fingerprint. See this article for a paper on User re-authentication via mouse movements.