I'm still hanging on to Hartline. I never really expected him to be a weekly starter, but I think you could do worse with a bottom of the bench boom/bust option. For me, he's probably the #6 option on my team behind Harvin, Marshall, Nicks, Stevie Johnson, and Crabtree...but in a must win situation or a difficult matchup, I may be willing to play him ahead of Johnson or Crabtree.
He's definitely a matchup play at this point. He isn't a skilled enough player to put up big numbers against elite CBs or top pass defenses. The good news is that I only see a couple tough matchups remaining on the Dolphins schedule for him. Week 8 against the Jets, he'll match up against Cromartie. Week 12 and 14 he'll play the Seahawks and 49ers. Other than that, he only plays one other pass defense that's in the top half of the league (the Colts, #15 against the pass).
I think he's a solid buy who you may be able to get for someone sitting at the bottom of your roster.