If you're one of those lucky folk whose loved-ones have the disposable income to have been able to have bought you a computer for Christmas - congratulations!
As a former major electronics retail store employee, there are a few things the big-name stores probably tried to sell your gift-giver on: warranties and pre-setups. There are good and bad things about both of these, so I can't unequivocally endorse or denounce either.
Warranty (aka - you break it, we might fix it):
There are a few important considerations for warranties. For starters, how long is it? Are you conceivably going to still want this device at the end of the one-year manufacturers warranty? If it breaks in one year, are you going to want it fixed or will you want to upgrade?
Also, what does it cover? If it just covers manufacturing glitches, then it might not be worth your while. Any major bugs should be evident within the first year. However, batteries are a different matter. Your battery, with normal usage, will more than likely die before the first year. If you don't care to find out how to preserve your battery life, make sure the warranty covers replacement and that the cost of the warranty isn't above the cost of the battery if that's your only concern. Makes sense, right?
Is it a repair warranty, or an outright replacement guarantee? I know of one particular store that offers a warranty that covers replacement even if you're an irresponsible schmuck and pour a keg on it before tossing it down a flight of stairs and allowing your dog to chew on it. If you look like that kind of schmuck (or your sibling, roommate, partner, etc is), consider that warranty.
If they got the computer recently enough and you decide you do/do not want the warranty and it has/ hasn't been purchased, you usually have 14 - 30 days from the date of purchase to have it added/ taken off the bill. So, it might not be too late to change your mind.
Presetups (aka - do I really want to spend an hour on Christmas morning installing Win7?):
Computers and laptops nowadays come with Windows 7 preloaded in lieu of installation disks. It's not configured, though, so when you bring it home and turn it on for the first time you have to go through the steps of setting your time zone, giving it a computer name, connecting it to your home network, etc.
This isn't an insurmountable task, by any means. If you're literate and have the patience, you can quite easily do this yourself. If you consider a computer to be a scary, mysterious box of worry and woe, then maybe you should have someone else do this for you. If you have family members or friends who are comfortable setting this up for you and have the time, bonus. Otherwise, save yourself the stress and pay someone to do it.
Also, remember when I said Windows 7 doesn't come with installation disks? That means that if your computer encounters a catastrophic failure, you don't have the disks to go back to . If it's not too bad of a failure, you can reinstall Windows from the recovery partition from whence Win7 installed itself when you first turned it on. Otherwise, you might be outta luck.
What can you do about that? When stores preset up your machine, they include a set of recovery disks with your OS (operating system). Or, some systems have an option in Windows to burn the disks yourself. Here's how you do it with an HP.
Long story short, enjoy your new computers, you lucky SOBs. I'm gonna peck away at my Acer Netbook with a missing Windows key for another year or two until I have some disposable income of my own.
No hard feelings, though.