I've never spent an extended period of time at the level cap. I did reach level 70 before wrath hit, but due to the difficulties of gearing, I wasn't anywhere near able to even tank heroics, it was frustrating, and probably contributed to my taking a break from wow. That is not the case currently.
Things in Wotlk are different, and much more convenient for the casual player (as a side note, even though I probably spend as much time in game as many "hardcore" players, I consider myself casual because my goal has never been to tackle difficult content). Obviously a "fresh" 80 is not going to be able to immediately tank worthwhile heroics (I consider the worthwhile heroics as Utgarde Pinnacle and Culling of Stratholme, you know, the ones with multiple pieces of gear I actually want).
Upon reaching the level cap, I noticed I had a few options (I bought dual spec when it came out, so I have a retribution spec and set of retribution gear). First, I could continue questing, both the dailies and my uncompleted world quests for some easy gold. I could try to get into heroic instances as DPS and potentially get some tanking gear enabling me to later tank heroics. Lastly, I could level one of my many alts. Sadly, my options currently are about the same.
I'm not saying that I dislike "the game at 80". I finally got an epic flying mount (I can't believe I've spent seven THOUSAND gold since wrath on three items, how people justify those retarded motorcycles are beyond me). Usually my game time consists of "Hey, anyone feel like running a heroic? OK, guess I'll do my dailies, then go level an alt."
On the good note, I am about one heroic instance run away from honored with Wyrmrest Accord (yay easy tanking loot), I already have the pattern for the craften necklace and I have the crafted ring, boots and helm made already. I really am just a few pieces of gear away from being able to actually tank heroics (I'm looking at you sword and belt from UP and shield from CoS).
Also, spending more time with my alts has made me appreciate one of my lesser played alts. I have come to the conclusion that I really extremely enjoy my druid. My mage will probably hit outlands first, but it wouldn't surprise me if my druid beats him to 70(my deathknight will beat them both, but he started with a 23 level head start. He's been 69 for about as long as I can remember lol). While I had originally intended my pally to be a tank/healer combo, druids just seem better equipped for it (and I hear our GM complain about how handicapped pally healing is). Also, with blizzard's announcement of new druid skins, here's hoping they get rid of the ridiculous horns on the tauren cat form (how come night elf cat form looks so cool, and tauren cat form looks like a lion with some horns glued to his head like a cheap halloween costume - a Bull-lion).
Mid Afternoon Quickie
7 months ago