I had the same problem with Fedora 2, I assigned the x-sh and x-shellscript to an editor by mistake. First exit Nautilus, cd ~/.gnome/mime-info made a backup of user.keys and user.mime and deleted all the mime references (x-sh, x-shellscript) from both files. For example I deleted the following from user.keys:
application/x-sh
default_application_id=
category=Software Development/Source Code
default_component_iid=
description=
icon_filename=/usr/share/icons/gnome/48x48/mimetypes/gnome-mime-application-x-shellscript.png
use_category_default=no
application/x-shellscript
default_application_id=bsh
category=Software Development/Source Code
default_component_iid=
description=
icon_filename=/usr/share/icons/gnome/48x48/mimetypes/gnome-mime-application-x-shellscript.png
use_category_default=no
default_action_type=application
short_list_application_user_removals=
short_list_application_user_additions=bsh
I then deleted the following from user.mime:
application/x-sh
ext: sh
text/x-sh
deleted: moilegrandvizir
application/x-shellscript
ext:
I now have the default behavior for the File->Script
from Nautilus.