I guess the question says it all =/ Already installed Ubuntu Tweak and fiddled with the associations, but nothing is associated with Gwenview. Still, the rubbish bin opens up with it instead of nautilus. How can I fix it?
The problem may lie in this file:
You could back it up and then delete it. The file will be reconstituted as you open apps over time: "as you use the context menu or set new defaults the list will 'grow'".
More detailed information is in this Ubuntu Forums thread.
I had this problem when I upgraded 11.04 to 11.10 and clicking Trash in the Launcher opened Movie Player.