Do you remember those days when you logged in and did your 25 dailies while keeping your eyes open for a group of friends that might want to do the daily heroic? I have a route through Icecrown where I completed all my dailies in one to two hours. Once I found a group for a heroic, we had to get to the dungeon, wait for everyone to show up, and wait for people to go deal with noisy kids and dogs. Just assembling and arriving at the dungeon could take 30 minutes easy. Do you remember those days?
Now I log in, pop into the Dungeon Finder queue, a couple of minutes later I'm rushing through an instance with 5 strangers. Usually done in about 30 minutes. I feel no urge to do my Icecrown dailies anymore. I have realized that a lot of the time I spent online was "busy work" I did while waiting for an opportunity to run an instance. There is no need to do this busy work anymore. So, I'm not online as much.
This is great for the casual player that only wants to play a few hours a week. I confess that besides my main Big Healer, I have two other max level healers, a Druid and a Priest. I don't play them often, but once or twice a week, I'll log one of them in and run a heroic. Although geared well enough for heroics (a mix of heroic, crafted, and badge gear), their gear is usually on the low level of the groups I get, but I still manage to get the job done. It's fun, challenging and only takes 2 or 3 hours a week.