This is my favorite bag for traveling with only a carry-on. The bag has comfortable shoulder straps for carrying as backpack which can be zipped away. I find backpack carry is much more comfortable to carry any sort of weight versus messenger style or a shoulder strap, which this bag can also do.
The organization on this bag is really nice. There's a padded laptop compartment at the back so you don't need an extra bag for that. There are two pockets at either end, one large enough for shoes, and the other is perfect for stashing your liquids. Finally, the outer pocket is good for your in-flight needs (magazines, iPod, etc.).
The bag is very well made, as you would expect from Timbuk2. It's a clever design and really useful item.