Steam brought a bad habit from Windows to Mac OS X — placing program related files into user’s documents folder. The folder is called “Steam Content” and it appeared in “Documents” right after I installed Steam onto my Mac yesterday.

However, you can easily hide or move it.
Hide it
Launch Terminal.app and paste the following into there:
setfile -a V ~/Documents/Steam\ Content
The folder should disappear immediately. To make it visible again, use:
setfile -a v ~/Documents/Steam\ Content
To view it in Finder while it is invisible, use:
open ~/Documents/Steam\ Content
Move it
Alternatively, you can move it to another place (be that another folder or even another partition). After moving you would have to create a symlink (sort of a shortcut in Windows’ terms).
For example, you can move it to user’s Library folder (the first line moves it, the second line creates a symlink and the third line hides the symlink in Finder):
mv ~/Documents/Steam\ Content ~/Library/Steam\ Content
ln -s ~/Library/Steam\ Content ~/Documents/Steam\ Content
setfile -P -a V ~/Documents/Steam\ Content
It’s not necessary to move using the Terminal.app — you can as well just take and drag in Finder to wherever you want. In this case, disregard the mv ... command and use only:
ln -s NEW_LOCATION_OF_STEAM_CONTENT ~/Documents/Steam\ Content
setfile -P -a V ~/Documents/Steam\ Content
If you don’t know the exact new path, just drag and drop Steam Content (while it’s in the new location) to the Terminal.app window.
Thanks for all this info.
Just to let you know, Valve is actually fixing that issue, and well aware of it: http://store.steampowered.com/news/3857/
And to anyone else who might have got here hoping for a solution for dropbox, well, none of this worked on my mac to prevent Dropbox from syncing it along. Only solution I’ve found is either quitting Dropbox while Steam is open or, the actual way I did it, moving Dropbox away from Documents (I actually removed Documents from inside my dropbox, but that’s beyond the point).
Thanks for information.
my terminal says: setfile: command not found
any idea?
You don’t have XCode installed (forgot about that aspect, sorry). You can download SetFile and extract it, for example, to the Desktop.
Your command would start with:
~/Desktop/SetFile
instead of just “setfile”