Reposted from the other thread.
Ch-ch-changes
Changes people noticed so far.
Akuma: Demon Flip: A new command throw that Akuma has had in Street Fighter titles.
Tatsumaki Zankukyaku: When used as an assist, knocks enemy away rather than knocking them down.
Arthur: More health (?) Arthurs air S makes him dive to the ground very quickly now, allowing him to combo easily. Can throw 3 lances (?)
Captain America: Double Jump: Captain America seems to have a double jump now.
Shield Slash: The speed of this special has been increased dramatically.
Overall Mobility: Captain America, overall, appears to be a much faster character now.
Chris: Specials Startup: It is currently believed that the startup time on Chris specials are now shorter. This is not yet confirmed.
Dante: Combos: Dantes basic combos do not seem to be executed in the same way or have simply been changed completely. Hammer nerfed (?). Dante's j.S has more start up, Million dollars is more punishable and his st.L and st.S have faster startup.
Deadpool: Quick Work: The distance/range of this attack is said to have been increased. Faster Ninja Gifts (?)
Doom: j.C laser is faster
Dormammu: Flame Carpet: Pushes the opponent further away. Faster?
Iron Man: Uni-Beam: Overall startup and speed of attack increased and is now very spammable. Fly speed buffed, startup reduced?
Haggar: Lariat no longer a hard knockdown. Haggars f+H now causes bounce rather than huge hitstun (?)
Hsien-Ko: People on SRK noted a faster airdash and more damage to her hypers. SolarPowered, confirm if you can.
Magneto: Attraction: A new special move that resembles an orb which drags the opponent towards him. (A special)
Dash: Magnetos dash speed has been nerfed significantly.
Disruptor: Has had its speed reduced and is now slower overall.
Repulsion: A new special move that resembles an orb which pushes the opponent away from him. (B special)
Gravitation: A new special that Magneto can use to ground airborne opponents. (C special)
Air loops (mostly?) removed. Corner loops still work.
M.O.D.O.K: Air S Psionic Blaster
Morrigan: Finishing Shower: This hyper move has been had its startup and overall speed increased.
Phoenix: Air Limitations: Phoenix can now only perform one special in the air before dropping back to the ground.
Ryu: Chargeable Hadoken: A hadoken move that can be charged (like Zeros buster). Travels extremely fast at maximum charge.
Hadou Shoryuken: A brand new shoryuken that I have no current information on.
Shinku Hadoken: Can now reflect off of walls. It seems to reflect at a forty five degree angle.
Shinku Tatsumaki Senpukyaku: Now creates a large tornado when used.
Shoryuken: Ryus regular shoryuken can now be charged.
Overhead can be special cancelled into combos.
He has a hyper that buffs his other two hypers; this makes Shinkuu Hadoken ricochet off of walls, and Shinkuu Tatsu now creates a whirlwind that covers most of the screen; some believe it also buffs him in other, more passive ways
Sentinel: Sentinel Force Charge: Drones are deployed faster when used as an assist. Overall speed boost barring lasers.
She-Hulk: Overall Mobility: She-Hulk, overall, appears to be a much faster character now. Exchange glitch removed. Shorter slide.
Spencer: Death From Above: This new special attack is a damaging dropping attack from above similar to Super Skrulls meteor smash special.
Storm: New Wind Specials: Storm can now pull and push the opponent her using winds. Fair wind and foul wind. One pulls you a bit closer, the other much closer. Can no longer call assists when floating.
Super Skrull: Mid-air Meteor Smash
Taskmaster: Charge Stick: A new special where Taskmaster impales the enemy. Can easily be linked to Charging Star/Shield Charge. Charging Star covers much more distance.
Tron: Bonne Strike: This special now has a quicker recovery time.
Gustaffe Fire: The assist version of this has been nerfed. Tron Bonne is more vulnerable when called out to perform this assist attack.
Air H now pushes people much farther away limiting combo possibilities.
Viewtiful Joe: Upwards Dodge: Joe can now perform a new dodge that enables him to dodge incoming low and mid attacks.
Wesker: Health Nerf: Wesker has been given a health nerf. Not sure how much less he has, but his health is said to be lower now. Allegedly even faster in XF Level 3. Forward air grab sends enemies full screen. Teleports slower (?)
Wolverine: Berserker Slash: This attacks speed has been reduced. Lost some of its invincibility.
Swiss Cheese: An oddly named new special move where Wolverine quickly slashes diagionally many times. Dive kick nerfed.
Wolverine is apparently at about 75% of his old overall speed. (TBC)
X-23: Rage Trigger hyper seems faster.
Zero: Rekkoha: This special now covers more ground, as it has become wider.
Sources:
http://rev-depot.com/2011/07/20/ultimate-marvel-vs-capcom-3-info-post/ and
http://shoryuken.com/forum/index.php?threads/umvc3-list-of-changes.141620/page-5
http://www.neoempire.com/forum/showthread.php?t=11445 and discussion in this thread.