I'd picked up a BBP Industries backpack about a month before the rMBP hit. It's awesome.
Horizontal fit (left to right) and vertical fit (top to bottom) in the laptop compartment is just about perfect. There's a bit of extra space front-to-back due to how thin the rMBP is, but in practice it doesn't seem to move around much at all.
Construction is very good. The exterior is durable, and the interior of the laptop compartment is quite soft. (Durability was important for me, as I'm apparently very hard on bags)
Great amount of padding on the back, which partially conceals a handy pocket that's just about exactly the size of a 3rd-gen Kindle with the lighted case.
The secondary compartment fits my iPad, various cables, PS Vita, a backup USB disk, and has room to spare.
Definitely a bag I'd recommend to others.
http://bbpbags.com/industriesbackpack.html
(got mine slightly cheaper on Amazon)