The Sightless Eye has posted an interview with Blizzard's Bill Roper, talking to the designer about the current status of Diablo II (which was recently pushed back to early 2000). Here's an excerpt dealing with the current status of the game:

The Sightless Eye: I realize that this question has been asked before, but I know that it hasn't been for awhile, so I'll ask again. Can you give us the percentage of the game complete (approx.)?

Bill Roper: At this point we are content complete and are in the de-bugging, polishing, balancing and incorporating Battle.net technology phase. I don't think that I can really put an exact percentage to it, but we are very far along with the game.