Personally, all I do is set my monitor to go into standby after 20 minutes of inactivity. I don't need my computer to jump through hoops to render something that'll only show up when I'm not around, as it doesn't make sense. If I'm going to tax my system, I at least want it to be with something I'll actually get a chance to look at, if not interact with. Besides, screensavers suffer from "acute novelty factor syndrome," i.e. the first few times you use it, it's "WOW THE TOASTERS ARE FLYING AWESOME MAN," yet after a while it quickly becomes boring, if not annoying. (the annoyance factor kicking in if you foolishly and stupidly choose a screensaver that utlizes sound effects)

The idea of using a slideshow screensaver for presentation purposes is quite interesting to me, though, in that it's giving an actual function to something I've often found functionless. (Yes, I know screensavers were/are designed to prevent monitor burn, but you can accomplish much the same thing by shutting off your monitor or having it go into standby.) I might have to look into this further...