Interesting!
For me, I was in a guild with two raid groups, and it was very well organized, but going for P1 into P2 was a massive change to time requirements.
Going from being able to raid log for 2 hours/week or so per character for all of P2 raid content to more like 12 hours/character for both 25 and 10m Ulduar progression was just way too much time, and people could no longer justify it to their families.