This is an interesting discussion for me as I live in Colorado and have never had any real problems at altitude. I have witnessed it first hand in other people and it can be kind of scary.

I have climbed several 14'ers and I also compete in long distance bike races. One of the internet groups I belong to is all about the now famous (Lance Armstrong factor) Leadville Trail 100. This race is all about altitude as it starts at over 10,000 ft. and has about 14,000 ft of gain during the course of 104 miles of racing. The altitude during the race doesn't seem to be a big factor for me, but I have noticed that I don't sleep as restfully my first night at 10,000 ft. I live at 4,500 ft so this is quite a jump.

True altitude acclimation takes at least 3 weeks and as far as athletic performance goes (not necessarily applicable to backpacking) you will perform best if you just show up to race on race day. Spending a few days at high altitude will actually tear your body down and wear you out. You will not sleep restfully and your body is burning itself out trying to adjust to the thinner air.

As far as backpacking goes if you have the time to do it a slow increase is best as your effort level isn't nearing your anaerobic threshold. Go high during the day but sleep lower down. You won't be as beat down if you sleep lower down as you will sleep much better. The difference between racing and backpacking is huge unless you plan on blitzing Whitney in one big fast push.

No caffiene, no alcohol, and lots of water all seem to help. Good luck to you.

-Skippy