> an accidental middle-click-to-paste in the middle of page is highly confusing to users.
I agree, especially when combined with the middle click on a URL opens a new tab instead of a new window. managing to miss the URL takes you off to some other page (or an error, depending on what's in the clipboard)
this is always one of the first things I disable on firefox, unfortunantly it's only possible through the about:config interface (search for middle and then change middlemouse.contentLoadURL to false)
But this is just a case of one application (firefox) doing silly things.