Tom is designing a smaller version of the Brain Bag that should debut late this fall. Another option would be the Smart Alec, our smaller backpack. It's the one I use and I find it to be just the right size.
That's interesting because as much as I love my Brain Bag, I find that more often than not, it has too much room. It's great when you go away for a weekend or something though and you can just stuff it with everything! But when I'm going about town or traveling for a day or something, it's a little bit much to carry around.
What sort of dimensions are we talking for the new Brain Bag? I assume you'll still be able to carry a portable computer but will the 15" MBP be too big?