Nebraska has decided (1:23 PM) that it will apply for membership into the Big Ten. Given that Jim Delany has basically said that the only teams that should be applying are those who are invited to apply, I think it's safe to say that the Huskers will be the second team to bail from the Big 12.
There is technically a chance that this won't happen. Nebraska is, after all, only applying to get into the Big Ten. It would be pretty cold for the Big Ten to invite Nebraska to apply and then turn it down though, so I think we can relegate that scenario to the sidelines.
If Chip Brown's reports are true and the Big 12 South schools think the conference can't be saved without Nebraska remaining in it, then this is the official death knell of the Big 12.
UPDATE
Some official-like wordage from the Omaha World-Herald, who broke the story:
...from Lee Barfknecht:
Nebraska has officially accepted an invitation to join the Big Ten Conference, The World-Herald learned early Friday afternoon.
Two sources from conference offices said that Big Ten Commissioner Jim Delany contacted Big 12 Commissioner Dan Beebe on Friday morning to inform Beebe that Delany had officially invited Nebraska to join.
A source with direct knowledge of the situation said Nebraska accepted.
UPDATE 2
Nebraska President Harvey Pearlman has asked the Board of Regents to authorize him to move NU to the Big Ten. He's "optimistic" that Delany and company will accept. He can't resist a swipe at Texas though: "One school leaving does not destroy a conference... Nebraska did not start this."
Pearlman confirmed the existence of a Big 12 ultimatum. He was told that the Big 12 South teams would stay if Nebraska did, even if Missouri and Colorado bolted. Pearlman wanted those six then to assign their media rights to the Big 12 for the long term to prove their loyalty. Texas said no, and so Nebraska decided to leave because it felt it was in a "vulnerable" position in the uncertainty.
Pearlman expects to be in the Big Ten for the 2011 athletic seasons.
SIDE NOTE
Chip Brown is Twittering out to the world that officials from Texas, Texas Tech, Oklahoma, and Oklahoma State have told him this announcement from Nebraska means they are going to the Pac-10. Conspicuously missing: Texas A&M.