Inspired by this submission:
What I'd like to see is a view mode (in addition to the current icons, tiles, details, list etc) that would dynamically resize each icon based on its popularity (ie. number of times clicked). This basic idea is the same as a tag cloud:
The Start Menu already tracks your most recently used shortcuts (apparently incorporating the popularity of the program as well, to some extent), so extending that feature to be systemwide shouldn't be too difficult.
This has myriad uses. You could use it in Windows Explorer, making documents you open most often larger and thus easier to target. You could use it on the desktop, making your most popular shortcuts larger. It could be incorporated into other programs, like Media Player and Media Center (resize album art based on number of times played), as well as 3rd party products.
And, lest someone misunderstand, this would in no way be mandatory. It needn't even be the default mode. But it'd be user-settable for each individual folder, if they so desire.
See screenshot for a rough mockup.