I think I've found the limits of Video Mode Ultra -- when we first hard in the 3.1 patch notes that Blizzard was adding in a superspecial video mode for high-end computers to use, I was excited. I just recently "updated" my PC (read: "it broke and I had to spend a lot of time and money to fix it"), and it's been running like butter, so I was interested in putting it to the test. The day after the patch dropped, I flipped the switch to Ultra, and had no problems -- until this past Saturday. While wandering around Dalaran, I noticed my framerate had dropped quite a bit. I lowered a couple of the environmental settings just a bit and I was fine again, but apparently even with a 2.5 GHz quad core CPU, 4gb of RAM, and a GeForce 9600GT, Video Mode Ultra is still just a little too hardcore for me.
What's interesting is that I ran Wintergrasp a few times before having those slowdowns in Dalaran, and never had a problem. But then again, Blizzard did say that they had spent a lot of time making sure Wintergrasp was streamlined enough to run huge battles with minimal slowdown, so maybe Dalaran didn't get that same makeover. And I should say as well that I had no issues anywhere else in the world -- even my Naxx run the other evening looked perfect with Ultra flipped on.
Having a "future" graphics mode on PC games is nothing new -- for most games, the highest graphics setting is usually "experimental," so there's a little leeway in terms of release time (the game looks good with current hardware, but even better with next year's gear). And Video Mode Ultra is just that -- Blizzard trying to send a shot across the bow at those who are already saying the graphics look a little dated.