Fun fact: The last time the Best Actor winner at the SAGs did not match up with the Oscars, was when Johnny Depp won over....Sean Penn in 2003.
Slumdog has all the momentum right now, yet it hasn't suffered a backlash like so many other frontrunners do. I really can't see anything derailing its chances. Button didn't get great reviews, Milk is gay, no one cares about Frost/Nixon and The Reader doesn't exist.