Hi,

Users expect, that the action (which application is to be run) is
determined by file extension. 
The mime-type idea is a terrible thing for a normal user. They simply don't
understand it.

It should be configurable (per user or per system) if mime type or file
extension is to be used.

The ideal would be if:
1. switch to recognizing file type by it's extension.
2. as in 1 but if one extension is used for different mime types, then
in such case nautilus should detect mime type from file content. This
should be controlled by user - eg. if user wants to associate an
extension with another application, he would get dialog box with
question if previous association is to be dropped or if the mime type
for this extension should be detected by file content.

This should also improve performance of directory listing a lot!