An update to Flickrdesk. There's now a setting for minimum width and height: any images smaller than this will be dropped, and larger images will be resized to fit the desktop.
The script also uses sips to a) add an icon to downloaded images and b) add the corresponding Flickr URL into the comments field of each image. This makes it easier to browse the photo storage folder in the Finder and get back to the Flickr page for a photo that you like.
Download, and don't forget to edit the file to use your own favourite tags to subscribe to.