It's nice that you are returned to the preferences page after saving, but without any information about if it actually got saved I think more people than me will save once more just in case, at least the first couple of times.
Just a note in red at the top of the page would be enough, or maybe next to the button.
Also, why not save using AJAX and just update the page with the info, and possible with warnings as well. Not that important though, but could be a nice addition for a future version.
