Pac-12 plays the role as linchpin in the BCS
Why am I saying this? Well there will likely be six SEC teams in the top 14, therefore for of them won't be going to the BCS. That leaves 10 teams for 10 spots. However, the Big East champion will be outside the top 14, so it is really 10 teams for 9 spots.
Assuming the BCS is occupied by 2 of the SEC teams (let's say Alabama and Georgia), the Big East champion, Big Ten champion (let's say Nebraska), the ACC champion (let's say Florida State) and the Big 12 champion (let's say Kansas State). That is 6 teams. Notre Dame and Oklahoma are safe bets for at-larges. That is 8 teams.
So who gets the final two spots? It comes down to the Pac-12. Oregon is going to go to the BCS. They are too talented and exciting not to. If they win the Pac-12 (which will require Stanford losing to UCLA this weekend and them beating Oregon State this weekend and UCLA next), then the last at-large will likely come down to Clemson or Stanford.
However, if Stanford or UCLA wins the Pac-12, thus taking the conference's auto bid to the Rose Bowl, Oregon will take that last at-large bid and Clemson will be shut out of the BCS (as will the Stanford-UCLA loser, in all likelihood).
Sure, there are other scenarios that screw with this. Most notably Michigan, a very attractive at-large team, slipping into the top 14 with a win over Ohio State, or Oklahoma losing and falling out of the top 14.
Another nightmare scenario for at-large hopefuls is an undeserving team stealing a BCS bid with a conference title game win. For example, if Georgia Tech were to win the ACC title game, it would go to the Orange Bowl, sending ripples through the entire ecosystem.
Morals of the story, the Pac-12 is critical, Clemson fans need to root for Oregon and for all the other favorites and UCLA and Stanford would be best off not leaving their BCS hopes in the hands of fate. Instead they should earn berths.