After the Catalyst 3.7 drivers (the ones where they disabled AA for Splinter Cell and Race Driver) it stopped working.. In most levels.
So far, I'm on the ~10th level and it's worked in three of them. I don't know what the deal is.
From an extensive thread over at Rage3D, I find that the drivers are programmed to disallow AA from working when certain DX functions are called upon by a program.. namely the functions that cause artifacting/corruption in Splinter Cell and Race Driver when AA is enabled. Unfortunately these are the only two games that experience this, while an entire host of other games (five by my count so far, Chrome included) can not have AA enabled with them after the 3.7 drivers, where AA worked just fine in them before.