If I've got a folder called mywebsite.com, for example, .com will appear in the extensions column.
Could you add the option of hiding "extensions" for folders as it isn't really an extension but part of the name.
Personally I don't use XP's zip folder capability.
This could be overcome by an inclusion/exclusion list:
Disallow *
Allow .zip
But only have this for folders and not files.
Personally I have no need for this column anyway so I've removed it from my view. Showing the extensions in the name and sorting by extension is of course still no problem without it.