Scratch

It would be great if leaderboards were added to the scratch website. This is how I propose they work:

Add a new block to scratch.
[submit score x] This block would submit the scratch user name along with the score variable. If the submitted score beats any of the current scores, the new entry will be placed on the leaderboard.

This feature only works online.
The feature only works online, so offline users will not have their scores submitted. This also discourages scratch programmers from posting broken programs which only work when downloaded.

Leaderboards only appear if they are used.
All projects will not use leaderboards. They are mostly for posting game scores. A project will only display a leaderboard once the first [submit score] is called. Therefore programs in which leaderboards don't make sense wouldn't have them.

Avoid spamming hiscores.
To avoid a poorly written scratch program spamming the website, there can be an internal control that turns off the submit command if called too often in a program execution.

Leaderboards would encourage competitive play on game projects and give players who do well bragging rights and perhaps more traffic on their own projects (if there was a link back to the user's page from the leaderboards).