BF2 kind of had a similar problem. Some of the rewards required ridiculous feats, like repairing 40 vehicles in one round, which is nearly impossible during the course of normal gameplay. It had the effect of encouraging some people to not even play the game and instead do all kinds of ridiculous things like park a jeep halfway into the water so it took damage and then repaired it for the whole match. Certainly doesn't help the team.
People use to make specific servers for farming stats such as "knives only" "pistols only" etc... It was pretty lame. I expect the same from BF3 based on DICE comments.