One big problem about expansions is that it basically makes old content obsolete. I played WoW from the beginning, and leveled many characters. One thing I noticed is that everyone seems to be concentrated on hitting that max level, so nobody really gives two shits about past content. Cataclysm will help renew old interest with heroic versions of classic dungeons, but really that's just because you are probably going to skip every dungeon upon leveling since it's near impossible to get a group for it.
I quit WoW, however, because they def made it too "casual friendly" for my liking. I got to a point where my 80 warrior was pimped for tanking and dps, so I decided to make a Death Knight (I waited a little while so there wasn't quite as many DKs leveling) and within two weeks of hitting 80 I had him in full epics too. I should point out that I've never been in a raiding guild, and managed to get a lot of the epics by organizing PuGs. The original WoW was way harder, and even in BC you at least needed to get keyed for stuff. WotL ruined it all for me. I also went blacksmithing crazy on my warrior, with an average of 70-130 items on the AH at anytime, which according to my stats averaged me 3.3k gold per day and I made so much gold... I'm not sure how much because after 200k it went negative and I couldn't figure it out anymore... I had a Mechano Hog on both my characters, plus a traveller's mammoth on my warrior and 20k to buy a 2nd one on the DK. That's when I quit.
Actually, I'd sell my account for $600.