(just copying what we talked on irc)
We're talking here about two bugs.
#1 feedburner fetches the guid and overrides the link with it
#2 some browser (versions) seem to use the guid instead the link.
(the specification says: "There are no rules for the syntax of a guid ... If the guid element has an attribute named isPermaLink with a value of true, the reader may assume that it is a permalink to the item, that is, a url that can be opened in a Web browser, that points to the full item described by the <item> element." -- RSS 2.0 Specification (RSS 2.0 at Harvard Law)