The TiBook snugly fits inside of the brain cell and the cell has hard padding on all sides. It snaps inside the brain bag via four snaps such that the weight of the laptop is evenly distributed across my back.
The brain bag is, by far and away, the best and most comfortable bag I have ever owned or tried. Highly adjustable, roomy, and fits on the body perfectly– even a heavy load is easily balanced and sits comfortably on your back for long periods. It is also extremely well built.
I also picked up a Snake Charmer from Tom Bihn. I keep a complete set of cables, a small FireWire HD, and any AC adaptors in it at all times. The see through sides make it trivial to grab exactly what I need quickly and easily.
Tom Bihn is an excellent company. A friend put an order in with 2 day delivery because his current bag broke about 3 days before he was to travel for a week on business. FedEx screwed up such that the delivery would not arrive in time. He called Tom Bihn to ask if he could order a new set with overnight delivery and return the original order upon return from a trip, the nice folks at TB asked what was up and, upon hearing his tale of woe with FedEx, offered to ship him a new order overnight express without charging him a dime!