I think the “10- and 25- man raids in Cataclysm will share the same lockout” idea is a big mistake. I’m not sure why Blizz wants to add drama to EVERY 25man raiding guild. Sure the overall picture is great for 10man guilds, but it would be the same without this shared lockout as well. 25man guilds usually have smaller cores that also run 10s.. and the 10s are usually a lot easier/progressed.
Now, if it means you can switch back and forth within the same raidId, then might that be decent? e.g.- run 25man for three nights and then run 10man in the same raidid for a fourth or fifth night. I still think it would be drama-ful. If somebody runs the 25man the first night and then clears the place in a 10man on a second night there would be many a sad-face.