I made xscreensaver able to load images from RSS feeds. Test it for me? Let me know if you find any feeds that it screws up on, or if it seems to be re-downloading things too much, or whatever.

xscreensaver-getimage-file

On Linux, set imageDirectory in your .xscreensaver file to an RSS or Atom feed, and run any of the image-grabbing hacks (Carousel, GLSlideshow, etc.) For debugging, run it manually from the shell with -vv.

On MacOS, replace that file inside the .saver bundle and do:
defaults -currentHost write org.jwz.xscreensaver.Carousel imageDirectory URL