Im in a casual raiding guild and I find there is still plenty to do after 80. With the new expansion you now have a ton of different instances to do after 80, there are a ton of quest lines still to work on, you can work on your epic, faction to earn different recipes for tradeskilling. And thats not really getting into all of the raids you can join.
I have yet to find nothing to do on my lvl 80 characters and I've been 80 for awhile now. Still plenty to do. I know a lot of folks who feel the game only begins at 80