I'm pretty happy for just using delicious for that. It's always nicer when sites interact well with existing sites instead of bolting on a half assed version of the same functionality. Not to say that Paul's in the business of half assing things, but rather that it's slightly orthogonal to the main value of news.yc and already exists (done well).
Arguably search is an orthogonal constraint too, but crawlers inevitably are a few days behind the curve.
Yesterday, for example, I spent an hour tracking down this comment. Eventually I had to triangulate based on the users I remembered in the thread.
http://news.ycombinator.com/comments?id=13037
