From Nethaera’s blue post on the World of Warcraft forums:

The first of the refinements being made is that we’re combining all raid sizes and difficulties into a single lockout. Unlike today, 10- and 25-player modes of a single raid will share the same lockout. You can defeat each raid boss once per week per character. In other words, if you wanted to do both a 10- and 25-person raid in a single week, you’d need to do so on two different characters. Normal versus Heroic mode will be chosen on a per-boss basis in Cataclysm raids, the same way it works in Icecrown Citadel. Obviously the raid lockout change doesn’t apply in pure Icecrown terms though, as this change goes hand-in-hand with a few other changes to raid progression in Cataclysm.

We’re designing and balancing raids so that the difficulty between 10- and 25-player versions of each difficulty will be as close as possible to each other as we can achieve. That closeness in difficulty also means that we’ll have bosses dropping the same items in 10- and 25-player raids of each difficulty. They’ll have the same name and same stats; they are in fact the exact same items. Choosing Heroic mode will drop a scaled-up version of those items. Our hope is that players will be able to associate bosses with their loot tables and even associate specific artwork with specific item names to a far greater extent than today.

For me, at least, this is an interesting day to get this news. A few months ago, we finally took the plunge and joined a 25 man raiding guild after resisting it for a very very long time. Yesterday, some things happened inside of my guild which have led me to the decision of no longer doing 10 man raids on my main on a regular basis. It left me feeling a little lost, to be completely honest.

Do I still prefer 10 mans? Overwhelmingly yes. And because of this, I’m thrilled that 10 and 25 man raids will be sharing a loot table. I feel like now 10 man raiders and 25 man raiders will finally be on equal footing.

Will this change the way I choose to raid in Cataclysm? That I don’t know yet.

Expacs tend to shake up even the strongest guilds, and I don’t expect Cataclysm will be any exception. However, I’ve made a commitment to my guild and my guild mates, and if BoO stays a 25-man focused guild? I will continue to raid 25s on my main.

That said, this will encourage me to make sure I have at least one alt ready to raid the latest tier of content throughout all of Cataclysm because I want the opportunity to be part of a cohesive 10s team again. That is still where the majority of my raiding enjoyment comes from.  As the release date gets closer, I’ll likely be looking for people to commit to that cohesive team, and try to figure out what role will be most needed so I put my effort into the right character as early as possible.

I expect a lot of people are going to be upset about this planned change. Not me. I’m completely relieved. I’m looking forward to getting to do more with my alts, and have less chance of burnout on my main. I’ve been complaining about the disparity between 10 & 25 man loot practically since the day Wrath came out, so that is honestly the change that makes me happiest.