I'd class this as a problem. Delicious solves this by having the link on submission checking for uniqueness. If the link has been submitted previously you can't re-submit. The submission process should also be checking for link aliases (/index.html, index.htm, index.php).
Damn, missed that. How do you check, rectify for that? aside from honesty? It's a matter of the more authoritative source, so how do you check one link is more authoritative than another algorithmically?
If I were to tag this link, it would've been "Guy, Kavasaki, Eric, Schmidt, Google, CEO, Interview". There is a good chance Dan would have done the same. So tagging helps a lot.
Moreover, tagging leaves open the option to build recommender systems through collaborative filtering. I believe one of the reasons Reddit's recommendation tab was broken for so long (and still is) was because it was difficult to relate content without the use of tags.
http://news.ycombinator.com/comments?id=5471