Outside of just having a cool looking screen saver up for fun, I don't see the need. I would sleep the display, though, after a certain amount of time (I'm set at 5 minutes).
As above...Screensaver's were designed to protect CRT monitors from burn in and image retention...Now they are simply eye candy. I use the Itunes album art offering. Years ago we all used to gather round and install different ones from magazines etc. Now they are not required from a protection point of view .
You can still get burn-in on LCD's. I've seen it lots of times in data centers where a Windows or UNIX login screen is what's displayed 99.99% of the time. You can still see the shadow of those login prompts on the screen no matter what system the console is displaying. Looks pretty nasty.
It just takes much, much longer for it to happen on an LCD than it happens on a CRT display. Most people end up getting a newer monitor before then.