tho it has happened a few times watching vids on other sites..but not often

100% of the time youtube is a no go for new tabs using ctrl t

If you had clicked on the YouTube video (eg. to start the video playing) then the Flash probably has focus and hitting Ctrl+T will be expected not to work.

Click somewhere else on the webpage to give focus back to the browser, and then try hitting Ctrl+T.

FYI, this is the same problem for all the major browsers, including Safari, Opera, Firefox, and IE, not just Chrome. The Chrome bug report to track this is:
http://crbug.com/25756