I'll tell you why I wouldn't back Auburn... it's rather simple... REVENGE! Gators lost to Auburn last season and want payback. Also, Florida is giving up just 2.2 YPC and Cox isn't good enough to avoid mistakes vs. this quick defense. Tebow can add to his Heisman status with a big game as well.
The spread is large enough to make Auburn +18 look very attractive, but I see a woodshedding by a revenge minded Florida squad. Tebow throwing for 363 YPG and Auburn's weakness is their secondary.
Florida 38 Auburn 13 sounds about right to me.