I like to mantain only opentype kern feature and not use expanded kerning.
I know this creates a limitation but I tend to think things are evolving, I don't want to build fonts compatible with Win98 or something.
In other hand I know some famous software still lacks Opentype kern support, more notably Myfonts site and OS X Font Book (already filled a feedback form here http://www.apple.com/feedback/macosx.html)
What are your thoughts about this subject?