Today Google announced via the YouTube Trends Blog and Google+ that Google Trends has been expanded to include YouTube searches.
Now that YouTube searches have been added to Google Trends you can see what has been trending and spiking in YouTube search and the data goes all the way back to 2008.
Here is a screenshot (click to enlarge):
To use this feature first of all head over to Google Trends and search for something. Then on the left-hand panel under “Limit to,” choose “YouTube” to restrict the data to just YouTube searches.