I've been running around in World of Warcraft for about two months now, and I do like the game; however, it is a very different play experience from D&D, mostly because no matter what you do, it tends to go right back to the "grind" nature of most such games; you work various "fetch" quests and kill monsters to gain XP, so that you can handle more rewarding quests and monsters, so than you can handle even bigger monsters. Yes, one can roleplay in it, but the number of people trying to do so are needles in the World of Warcraft haystack. D&D, by its nature, has a "grind," but it takes far fewer iterations to get where you want to go, and the DM and players can set the exact amount of role-play that they want in between.
The main reason I don't want to see D&D migrate in a WoW direction is not because of "videogameyness" or any such phrase, but because I like its game system as-is, warts and all, and one of those warts is the resource management elements being phased out with the "per encounter" system. As time goes on, those elements will get fewer and fewer, and the emphasis will likely be placed on "how fast in game time you can get back to fighting."
With per-encounter, many such old classics as the time-sensitive adventure, or things such as Gary's old Slavelords dungeons will become VERY hard to pull off. There's no need to be careful in combat if every combat you're entering at near-full strength; If the island is blowing in one hour and you're stuck in its bowels, there's no reason why NOT to stop for that one or five minutes and regain all power.
If 4E does a good job of mitigating my fears on this area, I'll be leading the pack in the buying binge; I still DO like the idea of a character slowly regaining their resources over time, but for me under an hour is way too fast for my tastes. If it doesn't mitigate my fears, then it won't be my game of choice, and 3E and other systems will be.