Valve said they are giving duplicates for "item trading" in the future, no idea what it means. But it's taking a lot of the fun out of getting achievements for me. Not only is my heart not into playing sniper or spy, but there's no way to specifically try and get the new unlocks even when I'm not those two classes, either.

I don't think achievement servers (bad though I think they are) were bad enough to warrant this really arbitrary system that discourages planning or going for the neat things in the achievements.