YouTube Videos in Mahara via Chrome
(Taken from an e-mail reply to a student who was unable to use Chrome to view the YouTube videos embedded in her portfolio.)
During the recent site move (Fall 2012), the server configuration settings were enhanced to align them with IET's standards. Normally the change is fairly transparent to site visitors/users (e.g. The most obvious change would be the site address changing from http://... to https://...). Content from YouTube is considered unsecure content. I suspect you might be viewing your pages via a browser with the security settings set sufficiently high so that they're preventing you from seeing the videos on your pages.
I was able to view the videos using Firefox, IE (although it warned me about insecure content each time it loaded a page containing a video), but not immediately in Chrome. In Chrome, pages with insecure content display with a small, very subtle grey shield in the addressbar. If you click on the shield and select "Load anyway", the video displays successfully.