Where does Screensaver store images?
After scrounging around in plist files (thank you find and grep!), I found the beginnings of an answer, but I'm still a little confused.

It seems that those pesky images have been lingering around (renamed, of course) in the following directory:
~/Pictures/

Deleted them, and now when selecting any of the iPhoto portions of Screensaver, I get the appropriate error message:


-Yeah, that's the ticket!

I hope others will have more details, so I'll wait a couple of days before accepting an answer.