I too noticed this change, and I don't welcome it. I'd much prefer that the
guid be created from Permalink settings I have in the WordPress Options.
so wait... everything works just fine, but you think there's something wrong?
The links work correctly, but are not the pretty URLs that WordPress outputs so effortlessly elsewhere. It'd be much better to use the Permalink settings instead so that the
guid matches the Permalink (which is how it worked before I believe).
UPDATE Just found this ticket on WordPress Trac: http://trac.wordpress.org/ticket/6492 that concerns this exact issue.
The functionality did change recently, but according to WordPress devs, it doesn't really matter what the
guid is, as long as it's unique and never changes.
That works for me -- I just need to use a different method of using WordPress links on other sites. Right now I query the WP database and use the
guid as the URL. I should probably just parse the post slug and date and create the URL based on the Permalink settings instead.