Farmtown is not currently working on Facebook, in fact the bookmark has dissapeared from everybodies apps list.  And if you try to go directly to http://apps.facebook.com/farmtown/ you get this page could not be found or expired error message.

They are expecting to have this problem sorted in about 1 hours time.

If you would like some info from the lead developer on what is going on go here http://bit.ly/h1td9