As previously discussed I do believe that how much fun you have in any given game at any given moment not only depends on how good or bad the game itself is, but also on your personal history. Having said that, it is evident that the personal history of many players is rather similar in some cases. In the specific case of World of Warcraft today, it is clear that there is a large number of players who ran out of things to do in Wrath of the Lich King, and are all basically just waiting for the Cataclysm expansion.
I'm pretty much in the same situation, having run heroic dungeons often enough to equip 4 level 80 characters in full epic gear, and having seen (if not completed) all the raid dungeons in the game. I could still level my druid to 80, but from what I hear from the druid community that class has been seriously nerfed in Cataclysm, and anyway I never planned to use the druid as my "main", so it doesn't really matter whether he reaches level 80 before the expansion.
I am not in the Cataclysm beta, and even refuse to play patch 4.0 on the public test realms, as I predict that I'll run out of things to do in Cataclysm as well before Blizzard releases the expansion after that, so spoiling my fun early would not be a good idea. I'd just burn out faster. So right now World of Warcraft is pretty much on ice with me, playing only one or two hours per week nowadays.
The Cataclysm expansion is rumored to be released on November 2nd, but that doesn't mean nothing is happening before that. Already the first events in preparation of the Cataclysm happened, series of quests about how the gnomes and trolls are reconquering their homelands, in preparation of these classes in the future having their own starting zones instead of sharing a newbie zone with the dwarfs and orcs. There will be further events foreboding the actual Cataclysm. And of course we will get patch 4.0, already on the PTR, which will change many of the rules of the game, especially the talent trees for everybody, presumably in October.
One advice: If you still have emblems, consider exchanging them for heirloom items now. Patch 4.0 will transform your old emblems into the new token currency "justice points", or into gold for the older emblems. And you *can* still buy heirloom items for the new justice points, and you'll be able to gain justice points after patch 4.0, and before the Cataclysm expansion release. But from what I read the exchange rate is not very good, thus a heirloom item that costs lets say 40 emblems now will cost *more* than the justice points you get for 40 emblems in the future. Also justice points are capped at 4,000 on Cataclysm release day, so hoarding too many of them before the expansion won't be possible either.
Thus taking it slow right now, or taking a break from World of Warcraft, is probably a good idea if you ran out of things to do. If you are still having lots of fun, or started late, or are still working on something that is important to you, more power to you. But overall a certain lack of activity in World of Warcraft in the last months before the expansion is only to be expected. It's the calm before the storm, the expansion will probably bring news of new records in player numbers (aided by the recent release of WotLK in China), and phenomenal sales in the first week. WoW might be on ice right now, but it'll be a hot topic again by christmas.