Super Street Fighter IV: Arcade Edition is already the third iteration of the game in as many years. So as to not tempt a bloody revolution for a fourth revision, Capcom is making the version 2012 patch free. It's coming soon, and all of the tweaks have been detailed.
The full change-log is extremely detailed, highlighting a handful of balance changes for each character. These aren't broad sweeping changes -- more minutiae like changing the damage ratings of some attacks by 10 points, or increasing their stun effect slightly. The biggest changes come to Yun and Yang, who were widely regarded as overpowered on the high-level tournament scene. Most of their changes are weakened attacks, which should make the pros happy.
Check out the full change-log for a ludicrous amount of detail on the changes.