Truly a complete overhaul of the raiding system, it's a big change.
I have to say, I kind of like it. It will definitely save on burnout from raids, and if you don't make it into the guild's 25 man run that week, you don't feel left out if you're running a 10 man with the guildies.
This will ONLY work if Blizz does a good job matching the difficulty levels though. I have faith that they can do this.
On another note, the selective reading skills of people on this forum astounds me. 25 MANS ARE NOT GOING TO DIE OFF BECAUSE OF THIS. THEY WILL DROP MORE LOOT THAN IF YOU ARE RUNNING 2 10 MANS. NO, THIS DOES NOT KILL OFF HARD CORE RAIDING. HARD MODES ARE STILL THERE, AND THE DIFFICULTY LEVEL WILL NOT DROP FROM CURRENT LEVELS.
That is all.