How can multiple Mac users have the same iTunes?

If you want everything the same - content, playlists, ratings, number of plays, etc - to be the same for both of you, drag the entire iTunes folder, the one that contains the iTunes library files as well as the iTunes Media folder, to a shared location such as the Public folder. Then for each of you, hold down the Option key and launch iTunes. You'll be given the option to locate your iTunes library. Navigate to and select the iTunes folder in its new location.

Regards.

You should be allowed to drag to shared folders such as the Public folder. If not though, select the folder you want and secondary click>Get Info. Go to Permissions and adjust the permissions to that you have the ability to write.

Obviously, if you just need to copy those iTunes folders, you don't need the ability to write; just the ability to read, which you already have.

Besides, the /Users/Shared folder is indeed an excellent location for a shared iTunes library; I hadn't yet considered that. Ignore all the above instructions. First, make sure your two iTunes libraries are in sync. Use an external hard drive (or mess with permissions) to do what copying you need to. Then go into iTunes and iTunes>Preferences...>Advanced and change the iTunes Media folder location to /Users/Shared. All of your iTunes content should be copied (or moved) into /Users/Shared.

After that, do the same thing in the other account, and both your iTunes libraries will now be pointed to the same location.

This isn't "simple" because this wasn't something iTunes was intended to do. Like I'm saying, you can probably work around it, but you'd be using brute force.

Did you even read what I told you to do? Read it carefully and do exactly as it says. I never said to keep two copies of your iTunes content. Change your iTunes Media folder location to /Users/Shared. What exactly didn't work?

When changing permissions as described above: First, open the security lock, then change the privilege to "Read & write". Then click the gear icon and select "Apply to enclosed items". This propagates the privilege setting throughout the folder structure.
I did not play with adding music and so on yet, but I did gain access to the library across user profiles.

I was able to share the iTunes folder between multiple users as suggested by moving the iTunes folder out of the user directory, and right to the root of the disk in my case. Permissions did have to be adjusted.

As root I did something like:

# find /iTunes -exec chmod g+w {} \;

This seems to work as long as you are good about quitting iTunes in Account 1 before you try to open it from Account 2.

I also did not try adding music or managing the library at this point, so YMMV.