MGM Mirage has the line at 12.5, but you're right that just about everyone else has it as 12.
TradeSports, which is a pretty good indicator of the Conventional Wisdom since people are betting their money and not just expressing their opinion, has it as a 49% probability that the Pats cover a 12.5 point spread, meaning that the spread is set at just about the right point from Vegas' point of view--at that spread, it's viewed as a toss-up. TradeSports has a Pats victory as an 82% probability. These numbers haven't changed materially over the last 24 hours, so there's no sign that the spread is going to go down (or up) by a whole lot more, unless there is some sort of news event that changes things. It's noteworthy that this didn't budge during all of the hoopla over Brady's "boot," suggesting that these folks aren't gullible.