A DigitalPoint Forums thread asks if Google counts the links from YouTube videos.
The simple answer is no. If you look at a YouTube video that has a link in the description field, you will notice that in the code is a rel="nofollow". That means, Google and other engines will not count the link popularity from that specific link.
For example, take a look at my iPhone Popcorn Trick and view source and find "cartoonbarry.com," you should see the nofollow attribute applied here.
In addition, on my YouTube channel page you should see all links pointing to my sites are automatically 'nofollowed.'
So why add a link from these pages to your site? Well, if your video is viewed, why not leverage that traffic for your main site?
Forum discussion at DigitalPoint Forums.