As auser, I just want to say why I like the mime type. Not for jpeg or png that I can see anyway, but for pdf, odf or doc, that are shown as a generic icon. 
So the mime type avoids me having to go over the icon and see in the status bar blah.pdf or so, and know it is a pdf.

So yeah, the mime type is also in my case useless in 95% of the cases.
I don't mind a mouse-over effect instead, but the fact that I see the name of the file link on mouseover already covers that for me.

Benny