A lot of the guilds on my server (Cenarius US - Alliance) are having very serious issues getting enough people to raid 25 man content.

A lot of people are pretty bored with the game at the moment, or are busy with other things.

There's maybe 4 or 5 guilds who raid at prime time on a regular basis, with the few people who want to raid moving to them.

I'm pretty sure with Cataclysm, many or most will likely return to where they were, especially when interest is high again. We've got 5 or 6 raiders, who have their main raiding toon in a raiding guild, but who spend most of their time on alts who are still guilded with us. That basically says, they've only moved a toon, because they want to raid now and that's the only option.

There are so many attempts at PuG raids, pretty much primetime trade is inundated with people looking for more. I'm guessing its the same thing - people who want to raid, but who don't have enough in their guilds at the moment.