Freya recently posted a plea on the forums: Please, Blizzard, get rid of raid IDs. Raid IDs were put in the game as a way to make sure the best loot in the game didn't flow freely: rather than just running endgame raids over and over (and over), Blizzard put a hold on just how much one player can run them. If you get saved to a raid ID, you're usually out of that raid until things reset on Tuesdays.
But there are lots of issues -- at this point, agrees Zarhym, it's too easy to get saved to a raid. It's lame to jump in on a PuG where you do one boss and then the group breaks up for the rest of the week, and it's even lamer to have your raid ID ninja'ed by a few folks who decide they want to disband the group early. The mechanic is important to keep around, though -- if you think it's too easy to get endgame gear now, just think what things would be like if people could run Naxx or OS daily or even hourly.
But the actual saving is an issue, and one that the developers are working on -- they're planning on making it so that you would only be saved to an instanced when it's partially or even completely cleared (though that too would likely spread a little more loot around than wanted -- people would run the instance until the last boss and reset it to do it all over again). We'll have to see how this pans out.