How to Restore GNOME/Ubuntu/Nautilus Default Folder Icons

I was also looking for this. Turned out to be pretty simple. (if you know where to look, of course.. and that's the hard part)

1. Delete the file "$HOME/.config/user-dirs.dirs"
2. Run "xdg-user-dirs-update"

For reference, here's a "proper" user-dirs.dirs file:

# This file is written by xdg-user-dirs-update# If you want to change or add directories, just edit the line you're # interested in. All local changes will be retained on the next run# Format is XDG_xxx_DIR="$HOME/yyy", where yyy is a shell-escaped# homedir-relative path, or XDG_xxx_DIR="/yyy", where /yyy is an # absolute path. No other format is supported.# XDG_DESKTOP_DIR="$HOME/Desktop"XDG_DOWNLOAD_DIR="$HOME/Downloads"XDG_TEMPLATES_DIR="$HOME/Templates"XDG_PUBLICSHARE_DIR="$HOME/Public" XDG_DOCUMENTS_DIR="$HOME/Documents"XDG_MUSIC_DIR="$HOME/Music"XDG_PICTURES_DIR="$HOME/Pictures"XDG_VIDEOS_DIR="$HOME/Videos"

Solution from: ubuntuforums