I have recently had a problem with the places menu on Ubuntu 10.10, whenever i clicked a bookmark-

pictures etc.
It was opened with appearance preferences (Computer, Desktop etc worked fine just the folder bookmarks bust) so after scouring the net for two days i found that a bunch of people have had he same issue.
i found the solution

Simply run the following command in a terminal or via Alt+F2
gedit ~/.local/share/applications/mimeapps.list

This should pop up in the new terminal window that opens or similar to this

When the file opens, look for the line starting with inode/directory= and you should see the offending app listed at the beginning, ahead of Nautilus. All you have to do is either remove it or put it on the end of the line, making sure that nautilus-folder-handler.desktop is directly after inode/directory=.

Once you save and exit the file, your location launchers should be back to normal.

this information is courtesy of Ubuntu Genius
cheers peeps