http://www.capcom.co.jp/blog/sf4/development_blog/2011/01/18_3002.html
RYU
About cr.MK's hitbox
-Active frames reduced by 2, from 5F to 3F, hittable box is larger
-Total frames also reduced, from 23F to 21F, so you can stick out the move at a higher rate, but because the hurt box is exposed at the front, you have to be cautious
CAMMY
About Cannon Strike's height restriction
-During the rise of the jump, you can CS after passing around the 6th line on the Training Stage wall (after the 9th airborne frame)
-During fall, can CS while above the 3rd line (27F)
C. VIPER
About Burning Dance's (UC2) hitbox
-In Super, the hitbox was at the tip of the foot and only marginally larger than the hurtbox
-In AE, the hitbox is multiple times larger, making it easier to use in combos, as an air-to-air, etc.
GUY
About Guy's normals
-st.LP's hitbox is extended upward, and the hittable box is significantly reduced, making it rather good for a light normal
-Far st.MP is extended at the fist, making it easier to use as a quick poke. Coupled with the lowered hitbox for st.HP, you can land the Target Combo from a farther distance
BALROG
About Buffalo Head's damage change
-All headbutts now do 100 damage
-cr.LPx2 → cr.LK → HP Headbutt now does 134 damage (down from 162), 299 damage with Violent Buffalo (UC1) added to the end
Next is Ken, Vega, Rufus, Fei Long, Juri and Dhalsim.