About a year ago, Youtube - apparently prompted by Google - added the anti-web nofollow tag to an increasing variety of their outbound links (except for some links, such as those which were on content provided by videomaker.com, something that would seem to violate Google's own rules). You can see the salmon-colored excess here and here.

Now, visiting my barely-used Flickr site (flickr.com/photos/lonewackodotcom), I see that they're using that tag too, for instance on this: flickr.com/photos/lonewackodotcom/265708046 (see the link in the caption). I'm almost positive there was no such tag there before, but I don't know exactly when they added those or if those who buy a subscription or who have some sort of business deal with Yahoo don't have the tags on their links.