As a minor league-focused community, I think we're pretty much the last guys to give up on prospects in many cases. We have seen how prospect stock ebbs and flows, and how many talented players eventually get their chance, even if it takes years (see Jack Cust, Josh Hamilton, etc).
But it's a fact of the matter that some prospects just don't have what it takes to succeed in the major leagues, and it's wise to cut bait on them early. I'm not really talking about injured players here.
Who would you say is one prospect who was highly rated entering the season (top 100), who you think the ship has passed on and are no longer valuable, not counting injuries? I would say if I had to pick one off the top of my head, it would be Chris Carter of the A's. Sure he may get another chance, and he has great power, but he's already pretty old for a prospect and seems unable to keep a respectable K/BB at the major league level. Who is your pick?