so in THIS story from Kotaku, a new achievement in gears of war three will be the most difficult one ever to achieve. though - it more sounds like a time-grind to me
GoW has always had these types of Achievements. The first one had the "Seriously ..." Achievement, which requires 10,000 kills in a versus match. GoW2 had "Seriously 2.0", which needs 100,000 kills.