Just a question, since I'm sure other people might even want to know. Is just flicking the computer off pose any danger to it? I used to do that all the time and the computer ran perfectly fine, but then it started acting weird. Is there any specific reason why shutting down manually is usually a better idea?

If you are shutting it down just pressing the power button it can cause a few problems. I am sort of guessing here but it doesn't give it time to properly shut down. All the programs have to just shut off in the middle of what is being done and they aren't given time to stop everything and turn off properly. This can mess up these programs and other applications running. It could hurt your computer in the long run because some of these programs could get messed up I think because they will get lost or lose something. Shutting down the normal way I believe is better because it will give all programs a second to stop what it's doing and stop without any problems.

We've been having some trouble with our computer shutting down lately. It always stops on 'saving settings' and doesn't shut down. I always let it get that far before pushing the button to turn it off but my sister just turns it off with the button just in the middle of things.

I've found that her way really messes up starting up the computer the next time. So I guess if you are having similar troubles maybe you should try to figure out what's wrong (like I should!) in the meantime, try to shut it down normally and let it shut down as far as it will go before hitting the button.

Pressing the Power Button to shutdown isn't a good idea, in my opinion. The computer has processes running even when it is just sitting there idle, so when you 'power off', the processes don't terminate properly and you risk losing data. Also, there are some 'housekeeping' duties performed on a normal shutdown, so when you start-up again, the computer has to check a bunch of stuff (like the hard-drives) to make certain that all is in order before it fires up again. If nothing else, the time you take to do the suggested shutdown will more than save time on start-up next time. It also saves the machine's hardware a little bit of lifetime because the diskscans don't have to be performed. These points are valid on both Windows machines and Mac's because I own one of each. I don't have any experience with the 'nix systems, but I'm guessing these points would apply there as well.

If you just press the power button. it should instruct Windows to shutdown as if you clicked Shutdown (or Turn Off Computer) in the Start menu. Holding it down, however, will cause it to do a force shutdown, which can screw up your running applications and background processes. If you've ever used Linux before, you can see it ending various processes as well as sending the TERM and KILL signals to processes to those that don't shutdown on their own. This serves to tell you how much stuff an OS runs in the background.

I don't personaly it can hurt too much on a normal computer. But there is always risk, after all look at how often one's computer crashes... But like jlhaslip said there is cleanup that needs to be done, so even if it doesn't mess hurt your computer it will mess it up eventualyperhapse system file is open and being edited, not this perticular file is only a log file. When you force a powerdown it doesn't get a change to finish and save that file so it gets corrupt. This file like I said was just a log so windows will replace it with an empty one, however it will keep the old one and if you do this enough there can become some serious clutter.

Now What michaelper22 was saying about the power button acting like start shutdown only works on newer computers and only if it's been enabled.

Just turning off the computer does not harm the hardware, however it can result in software issues. The reason for this is that when a computer is shut down the cleaning up and shutting down actions of the programs are ran and thus they are exited properly and the things that need to be saved are saved. Therefore, if you have something open that needs to be closed and shut down, it can cause an issue

It works on almost every computer that's in our house. I can do that on my almost 8 year old HP computer, as well as our 2005 and 2006 HP computers. It's not that much of a recent feature. Also, by default, it will tell Windows to shut down when you press it.

Michaelhelper,
I'm running w98se on an old(er) Laptop and OS9.1 on an iMac (7yrs old) and both of them handle an incorrect shutdown similarly. They shut off okay, but both do a Hard Drive check the next time you startup. I'm sticking to my version on this one.
I think these things should be smart enough to close all the files and terminate the software processes which are running when you powerdown through the switch or on a power outage from the Main supply, but nobody asked me about it before they deveolped the systems, so I guess my opinion doesn't matter, but there it is...