I have been involved in a few of the other Boot discusins so I might as well my $0.02 worth here as well.
I will start by stating that I do work p/t at a shop but am by no means a certified boot fitter. But, I have been a die hard skier for over 40 years now and have gone through all of the beginner mistakes in regards to boots. I feel I have a good handle on when a boot fits my foot and try to use that experience when I give advice whether in the store or to friends and family.
Yes boots are the most important piece of skiing equipment. Why? Because they are the transmission that sends your leg and body motions to the ski. You want a clean transmission of leg energy to your skis to achieve quick response. So if your foot is moving around in your boot as you are trying to tell the skis what to do you are sending your message through a sloppy transmission making skiing smooth and precise virtually impossible. Therefore you want a nice snug fit. Not tight, but snug for most recreational skiers. Lets keep pros and racers out of the discussion.
Different boot styles will have different "lasts" to fit different foot shapes. If you are working with a good boot fitter, he will look at your feet ask about your skiing with similar questions for buying skis in order to determine what boot will fit those needs while also fitting your feet. If you are at a big box store and on your own, you need to try on a few different pairs and see what works but a fitter at an enthusiast shop is really the way to go. When trying them on and standing upright and not flexing the boots, your big toe should be lightly brushing against the end of toe liner. Then flex forward and your heal should be pulled back giving your toes plenty of room. Also pull the liner out of the boots and then put your foot into the empty shell sliding your foot forward till your toes touch, then bend forward slightly so you can peak down the back at your heal. You should have no more than a thumbs width of space, more than that, once the liner packs out, your foot will move too much in the boot. As boots do come in different widths, again with the liner out and foot in shell, move it side to side. You should only have 1-2mm of space between the widesst part of your foot and either side of the shell. Try to error on the smaller of 2 sizes as your liner will begin to pack out immediately and will grow 1/2 size by seasons end. It is easier to make extra room in a tighter boot than to make a big sloppy boot fit better.
As for custom footbeds, I always reccomend them and have been using them for almst 20 years now. They really do make a difference in all day support and comfort. Just look at the flimsy footbeds that come out of even $700 boots and they are cheaper than what comes out of $100 running shoes. Most shops offer a reduced price on custom footbeds at the time of boot purchase. You should take advantage of that.
Well that is about all I got. Hope it helps someone.
Edited by rickg - 12/14/12 at 8:18am