First off, the field is definitely top-heavy, with almost all of the at-large bids coming from the six power conferences. Of the 34 at-large bids, just three (Temple, New Mexico, and BYU) are from mid-major conferences. (To put this in perspective, there were four in the tournament last year, which was the lowest ever.) This is usually the case in the early stages of conference play, before the teams in deeper conferences beat up on one another. That said, I don't see the Big East getting nine teams, nor do I see the ACC getting eight. The Big XII getting seven is a little dicey too, as far as I'm concerned.
As conference play continues, I predict that Cincinnati, Texas Tech, Baylor, Miami, Virginia Tech, and Marquette will all struggle to maintain their positions in the field. None of these teams have strong non-conference resumes and they all will finish around the middle of the pack of their respective conferences. This should open the door for mid-majors like St. Mary's, Wichita State, Richmond, Rhode Island, and Xavier to sneak into the tournament. St. Mary's will most definitely get into the field with a victory tonight against Gonzaga, and they should stay in the field barring disaster in the WCC.
In theory, there should be a fair amount of mid-majors snatching at-large bids this year because of how turrible [sic] the Pac-10 has been so far. As it stands now, they would most likely only get one bid, which is unheard of for a major conference. Thus, the usual five or so slots normally allotted for Pac-10 schools should go to mid-majors, based on the fact that a lot of middle-of-the-pack teams from the Big East, Big XII, and ACC (mentioned above) will likely fall onto the wrong side of the bubble as conference play progresses.