I am a little surprised at all the negativity over this move. Yes, Harvin had decided to retire and yes, he needs to be handled with kid gloves, but he is talented and this team is flat out of NFL WRs - anyone that watched the last 2 games should understand that.
There was no magic trade for a good veteran WR that was realistically going to materialize, so this looks like about as good an option as they had. They did not have to give up any draft picks or players to bring Harvin back, as they would otherwise have had to do if they were to trade for a WR (and who really is available and at what price?)