If you have been following the news, you probably already know that there wont be much difference between 10 and 25man raids in Cataclysm. You will get the same loot, just more in 25 and you will even be able to split a 25man raid lockout into two separate 10man lockouts. Off course, allot of hardcore guilds are against this.
Well, I'm not. You see, I'm the type of player that likes pretty much every aspect of the game. I don't wanna be awesome at just one part and only do that, I prefer to do a little bit of everything. This change is perfect for me. I will be able to do the raids for the week and I still wont feel to burnt out to do other stuff.
As for the completely hardcore guys, I guess they will have to find something to do with a few of those extra nights they will get.