Several sources have sprung up today, shedding light on the more secretive details in the cast. There's a more complete list put out by Mr. Wizard from shoryuken.com, and a smaller yet more comprehensive list compiled by Haunts from iplaywinner.com.
Bear in mind these are personal opinions, so take all the information with a grain of salt.
That said, it's of interest to note that not all characters received improvements as promised. Many of the weaker characters on the tier list still remain on the bottom end of the barrel, with little changed. Mr. Wizard had a hands-on copy of the final build, and noted that characters such as Guile, Ken, and Cammy took a turn for the worse, while others such as Chun Li held noticeable improvements (mostly in part to her new Ultra Combo).
Haunts (a veteran Street Fighter III player) held mostly favorable views on Makoto, Ibuki, and Dudley. They seemed slightly different from their previous incarnations, but were still very strong. He had mixed feelings on Hakan, but he felt very positive about Juri.
It still feels like there's a lot more to discover about the game, so until the game is released we'll just have to wait and see. Super Street Fighter IV comes out at the end of March.