How to open a folder (with GUI) from terminal?

gnome-open does not work for me on 12.04 but nautilus /path to open does work.

example: nautilus /home/john/Downloads.

If the question is how to open a file/folder, the answer is always xdg-open.

From man xdg-open:

xdg-open opens a file or URL in the user's preferred application. If a URL is provided the URL will be opened in the user's preferred web browser. If a file is provided the file will be opened in the preferred application for files of that type. xdg-open supports file, ftp, http and https URLs.

In this specific case the commmand

xdg-open folder

opens folder in your default file manager, be it Nautilus, Dolphin, Thunar or anything else.