To see the rest of this hint, read on.
You should ONLY put stuff in your /Library directory when you MUST. Sometimes you have things that need to be configured for all users or for boot time, but I have seen a lot of hints that suggest to install user level things in the /Library directory.
The /Library directory in your home directory (/Users//Library) is where 99.9% of all your configuration files should go. This is where everything that pertains to the way you like to run your computer goes. Application preferences go in here, added preference panes usually go here, and the list goes on.
So before installing anything in a directory for which there is a system level one and a user level one, ask yourself carefully where it should go. Don't just follow a hint blindly. If you have to gain superuser status (through su or sudo (to which su is better!)), be very careful that you are doing things right.
I understand that most users are new to UNIX, and it can be confusing. Most of you are all learning UNIX together, by exploring and trying things -- inventing as you go. Which leads me to note that many of the UNIX command line suggestions I see on here have better and faster ways. Sometimes I see things that are just downright improper hacks that work, but poorly.
Anyway, I guess the point is just to make sure that everyone is wary of what is posted on macosxhints.com. Not everything is right, and some thought should be taken before following a hint's directions. The people that post the hints may be just as new to UNIX.
Happy Hacking! :)
P.S. - Hope I haven't offended anyone; I'm not trying to sound like a jerk, just offering my advice.
[Sudo Editor's Note: Although paploo is correct, it should be noted that hints you see anywhere on the Internet that deal with the Unix under-pinnings of your OS X should be dealt with caution. One thing that makes this site so great, is that hints by those less experienced are often modified, corrected and enhanced by those more in the know, so we can all learn together and feel like we are not out on our own while experiencing a revolution in OS's.]

