Wow, things have been really busy around here, so thanks to MMO-Champion for making the post I was going to make.
In any case, MMO-Champion recently highlighted a new Add-on that is the NEXT BIG THING for raiding and guilds.
AVR: Augmented Virtual Reality and AVR Encounters, downloadable from wowace or curse.com.
It will be much much abused but can be configured to only accept files from the raid leader etc., and individual scenes can be erased fairly easily.
As mentioned over at MMO, the addon can allow you to put many things on your UI that will help with fights. My guild used it for the first time on Saturday's raid and it was amazing. In combination with other addons like DBM and vamp, it allows you to respond very easily to many fights. On Rotface it shows clearly where the ooze explosion will land. On Putricide where malleable ooze is coming. On Saph, we put circles where each frozen person was to stand. With the separate vamp addon, it will put an arrow on your screen pointing which way to run to the bitee a la quest arrows from questhelper (yay no more missed bites). AMAZING. In my experience, it used very little memory and should be easily implemented without excessive lag even by those with weaker computers. As MMO-champ mentions, the addon uses the Blizz standard API so it's not bannable, but it makes things so easy I can see Blizz trying to disable it in some way.
Of course, giving raid directions is not the only use for this addon.
One of my guildies put a very large phallus on the floor as we were zoning in to ICC, and a female character with girl parts exposed saying 'click my portal' on the portal. Unfortunately, my 10-year old saw it before I was able to figure out how to configure the addon to only allow files from the raid leader. Naturally, such shenanigans can add hilarity to any raid, but just be careful!
All in all, though, it will become part of the sacred canon of raid addons along with DBM, Omen, and Recount! Good stuff!