Hi all, lots of strange stings are happening on my Mac lately, but this may not be related.
However this folder: 
I have never seen before. Can anyone elaborate on what it is, and if it's nothing to worry about - or is 🙂
MacBook Pro, Mac OS X (10.7.3), 4 gig RAM
There are a number of important folders used by the system that are normally hidden, and the /private folder is one of them. In your case, that folder has now become visible. This does not in itself affect its function.
There are two ways that a normally-hidden item can become visible-
1) A global change in Finder's behavior ("show all files"), such that all hidden items are now visible.
2) A specific change only to the item in question, such that it it loses its "hidden" flag and is now visible even when Finder is behaving normally.
Your screenshot of the top level of Macintosh HD shows a "normal-appearing" /private folder, and doesn't show a number of other essential items that are always there but normally hidden. I therefore think in this case we are dealing with the second issue above. This "sometimes happens" for unclear reasons.
By example, one of my own bootable disks normally looks like this in Finder's list view:
.
.
One can make all hidden items visible to Finder , as per the first case above, by using a Terminal command or by using a 3rd-party utility program. If I do this, I see:
.
There are many previously hidden items now visible, and they all have a dim, ghosted look, including /private.
If I reverse that global change in Finder, and instead remove the specific "hidden" flag only on the /private folder as per the second case, I instead see this:
.
Of the normally invisible items, only the /private folder is now visible, and it is not "ghosted" - it appears normal, as did yours. So your situation evidently corresponds to this second case, where the Finder is functioning normally but the /private folder has lost its hidden flag. As mentioned, the reason is usually unclear.
You should be able to restore the invisibility of the /private folder with this Terminal command:
sudo chflags hidden /private
However as long as you remember not to go poking around inside the /private folder, it's also OK just to leave it alone.
I found this folder to be pretty big, like 50GB in size....do I need everything that's in it?
Normally that folder is hidden so at some point you turned on Show All Files. That is a normal folder that is on every OS X Lion install.
What is the Macintosh HD/private/ folder?
