This little Perl script called →ntrstng← will fetch the Flickr 'interesting photos' page from 2 days ago (to give the photos time to gather enough interestingness) into a specified folder, which you can then set as the image folder for your screensaver (that's what I'm doing with it, anyway).

Run it daily with cron and the old images will be moved into an archive folder, so the screensaver will have fresh images each day.

To fetch images from other Flickr feeds, use Flickrdesk.

Update: Peter Li has made a version of ntrstng that runs on Windows, under Cygwin (I haven't tested it yet).