You may want to try cleaning your windows temp folder.  One more thing that xl
does when you close it is to update your customized toolbar file (*.xlb).

You may want to use Windows start button|Find to search it out.  If it's large,
maybe excel is having trouble.

A few months/years ago, I went from over 450k to 11k (dumped the old and rebuilt
it).

And if neither of these help, maybe you can find something at these two sites
(Charles Williams and David McRitchie):

http://www.decisionmodels.com
http://www.mvps.org/dmcritchie/excel/slowresp.htm