Just include a link within a comment and that content will then be pulled into the comment stream. This is both a good and bad thing. People have been posting links to this content anyway, this just makes it more visual and convenient. The downside is of course that your comment threads now become a lot longer.
Time to break out that large external display.. or higher res MacBook Air.
“Today we are launching a commenting feature that allows you to embed videos, photos, or web sites in comments just by including a URL. Your comment will include a video player, a thumbnail of a photo, or a brief overview of the web site being linked to. If you prefer your comment without the preview, you can remove the preview with one click.”
More information @ Facebook