So we've had 2 days of Dragon Soul and a huge amounts of guilds have already cleared it all. I expect hard modes will provide more of a challenge. Mostly Harmles (yes it only has one s :O) has currently cleared 5/8 & hope to join the 8/8 crew before the next lockout.
The new dungeons seem to provide a simple method for people to gear up really quickly. Reaching an iLvl of 372 can be done in a day on a newly dinged alt, opening up the LFR Dragon Soul raid.
For a guide to some of the changes check this out: