Nautilus 3.6 comes with a "Recent" sidebar item (left sidebar: Places > Recent) which displays recently used files: documents, pictures, music, videos and so on.
This is a pretty big privacy issue because there's no option in System Settings (GNOME Control Center) to clear the Nautilus recent files list or to disable it.
So here's how to clear this Nautilus Recent files list and optionally, how to completely disable it.
Clear the Nautilus Recent Files list
To clear the Nautilus "Recent" files, you need to remove the "~/.local/share/recently-used.xbel" file - to do this from the command line, copy/paste the command below in a terminal:
Then, log out an log back in.
Restarting Nautilus didn't always work in my test, that's why I've recommended logging out and logging back in. After removing the "~/.local/share/recently-used.xbel" file, you can also clear the Recent files list by opening a file that's not in your recent files list. I know, this weird, but that's how it seems to work or at least, that's the behaviour I've experienced in my test.
Disable the Nautilus Recent Files list
To permanently disable any recent files from showing up in the Nautilus Recent sidebar item, open the "~/.config/gtk-3.0/settings.ini" file with a text editor:
and under "[Settings]", add the following lines:
If this file does not exist, create it. Make sure the header says "[Settings]" and not "Settings". This is how the file should look after editing it:
[Settings] gtk-recent-files-max-age=0 gtk-recent-files-limit=0
(there can be other items below these, of course).
To apply the changes, log out and log back in or follow the steps under "Clear the Nautilus Recent Files list" above.
Thanks to Vishnu NJ for the post idea (based on a question posted in the new WebUpd8 Google+ Community)