Thanks, John, et al! That's the definitive answer I was seeking.
As a predicted back of packer, I have worries about only having a bottle on hand at any given time, but as long as I'm not longer than 1 hour btw aid stations, it should be ok.
In response to:
Wide mouth bottle (singular). No contest.
Here is why:
1) Easy to refill (narrow mouth bottles are pain in the ass to refill. I can unscrew the top while moving, get it refilled it in 2-4 seconds and then start moving again while I screw the top back on.
2) Less weight. Who wants to drag 100oz of liquid up the hill when you can take a 16oz hand bottle and refill it in seconds at each aid station as needed? Even for the longest segment between aid stations (BC -> A-Frame), you can drink a cup of water at the station and then carry 16oz with you to cover the next 2.5 (or so) miles and then refill again at A-Frame.
3) It is much easier to monitor how much you have left and your consumption rate.
Whatever you do, avoid the narrow mouth bottles (used aquafina bottles, fuel belts, etc). Narrow mouth bottles are a royal pain to try and quickly refill, often taking 15+ seconds and wasting a lot of water in the process (says the guy who worked one of the aid stations for the past 3 years). Camelbacks are not too hard to refill for the volunteers but take the runner a lot longer to take off, pull the thing out, open the top and put it all back in again.
So please leave the cheap aquafina water bottle at home and go get an Ultimate direction Fastdraw Plus or a Nathans QuickDraw hand bottle. If you must use a belt, get one that holds a single wide mouth bottle and not a dozen little ones. Leave the FuelBelt (and clones) at home, the openings are not much bigger than the aquafina bottle.
Also, if you are using a hand bottle, only carry one. It is very hard to unscrew the top when you don't have any hands free. (A top level pro made this error last year. The aid station volunteers gave him a WTF look as he quickly realized his error. )
Note that you can still use a camelback as a nice bag to carry extra clothing (jackets, gloves, hat, etc). Just leave the bladder at home and stuff a jacket in that space instead.