What it does :
Removes unwanted ads and other layers over the YouTube videos.
How it works:
Searches every second for other graphical elementes over the YouTube video and removes them.
You can change the search rate by modifying the folowing line:

var loopTime = 1000; // check for annotations interval in milliseconds

How to use it:
-Install it
-Activate it from the GreaseMonkey menu
-Reload YouTube tabs