Mtn. Lion: I have also had some trouble with the screensaver. 2 displays: iMac 27” and 20” Apple display.
I have tried to set the screensaver to a folder that has several subfolders, but it will not recognize the subfolders. It only takes the currently selected folder. A minor problem, but it should be able to read the subfolders, IMO.
The bigger problem is that every time the computer starts the screensaver, whether I manually start (hotcorner) or it starts on the timer, it shows a black screen with the mesage Loading Photos. This takes it about 20 to 30 seconds, long enough that it is a distraction and annoyance. Why is this occurring? The images are in my Library on the startup drive.
Another issue is that both displays are showing the same images most of the time, even though set to shuffle. Sometimes different images appear, but mostly they are the same. Why?