I've been having a problem with screen effects since 10.1, all the way through 10.2.1. The machine is a slot-loading iMac G3/400 384 MB Memory, 60 GB HD, with the ATI Rage 128 8 meg card.
Anyway, the problem is that.. if any of the default screen savers such as "Forest", "Cosmos", "Beach", etc, with the transitions is run for a long period of time, the machine will suddenly freeze while the screen effects is in a transition. It no longer responds to any keyboard input or anything. At that point, a hard reset is needed with the button on the side.
Anybody else with this?