YES, this is a vital (even if it seems trivial) component of making your vshare site "viral". People tend to have short attention spans and could easily forget that they need to check on their videos from time to time. By having the system notify them that ..."Someone has just posted a comment on your video {videoname} - go check it out at {link-to-video}" - this will really add that vital stickyness factor to your site. Maybe the email could actually include the comment made by the commenter eg.:
"Hi Bob,
another {sitename} user, {username-who-commented} has just commented as follows on your video titled {videoname}: "{comment-posted-at-video}" - You can check it out at {link-to-video}.
Remember that having people comment on your video is a great way to get more exposure, why not go and post a comment on one of {username-who-commented}'s videos at {user-video-list-url} and get a bit of reciprocal commenting going. This way, you can help each other get more exposure for your videos ;-) (Hint).

Happy watching
The {sitename} Team"

This is a "Gotta-have" feature rather than a "nice to have" if you're looking for long-term repeat visitors to your site.