It's frustrating because Turner has shown some flashes. He had a multi-sack game and made some nice plays in run defense before his leg/ankle got rolled up on.
Personally I think it's a year too early to give up on him and we already have 4 DE's locked into the depth chart. If a DE is clearly ranked higher than others then draft him but I wouldn't go out of my way to get one just yet.
I agree on Turner, he gets pressure on the QB when he gets on the field. Fans tend to only remember sacks, but sacks tend to track pretty well with pressures over the long run (about one sack for every seven pressures).