One only has to check out their website at www.timbuk2.com to see the wide variety of customizations available. In fact, each order is custom made to your exact specifications via their intuitive online menu system. IF you need a real custom job, and you have the plans for it they will do their best to match up.

Durability:
Perfect 10. This bag will outlast the shoulders that carry em. Fully rain proof -- water will not penetrate the bag into your books, papers, or laptop! In fact if I dip the bag into the lake water will not seep in. There is an extra thick bag liner option that is just an overkill for most people, but the option is there.

Functionality:
Beats regular backpacks hands down. I confess I've never tried some of the messenger bags in the same price range but this bag does all that I need. I like being able to swing the bag around to get something out without taking the pack off my shoulders. Makes sense doesn't it? 'Messengers' have to do it all the time.

Please note that most of the weight does rest on one shoulder versus the other, but that really hasn't been a problem for me. Your mileage may vary depending on how much you carry, and whether or not you use the stabilizer straps.

It does stay put when I jump the curbs with my ATB bike.

Pockets:
There are pockets in there to hold pens, pencils, disks, etc. The system does work, but it is limited. There is also an outside zipper pocket, and little pocket to hold business cards.

Night Vision:
My bag is bright red and black. It also comes standard with 2 detachable highly reflective straps in the back. Excellent if you're a night rider or just don't want to be more visible to cars and trucks at night.

Other options:
Well besides customizing color, I also opted for the cell phone holster and the shoulder cushion. It added a few ounces to the packs weight, but they were welcome (if pricey additions). Now my cell phone is always within easy reach.

I give it a 9 in terms of functionality. They have addressed most of my issues with standard and optional components that can be purchased separately.

Value:
I'd give it an 8 only because I believe timbuk2 should discount their bags if you buy direct. Instead you have to look to other places to purchase the bag at a discount. I personally got mine at ebags. But you do get what you pay for, and that is one durable good looking bag.

Style:
10. Wide variety of colors, options etc available. Each panel is customizable! This is definitely something that you can call yours.

(update 9 years later).There are now even more customizable options and sizes available!
The bag is still holding up just like I remember it the first week.  Still durable, still waterproof, etc.  I don't use it daily anymore, but have recently started using it on my rides to the library (just a few miles each way), the grocery store, errands etc.  
I can see that if you were to leave the bag out in the elements in the recent 105 degree weather, you may experience some cracking on the inside which may affect the waterproof rating over time.  Note this is pure speculation on my part.  Regardless with a lifetime warranty on the bags I really can't see that being an issue.

Recommended: Yes