My experience
All my settings that "greatly affect" performance are at lowest or near lowest.
I can't remember my exact frame rates so I will have to re-post with that info. Away from the big cities everything runs great. I get a little lag in SW until the graphics catch up then it's fine. In Dal, when there are a lot of players in town, lag is fairly bad and riding a mount is almost unusable. When there aren't as many players around the lag is gone. All 5 and 10-mans run great. 25-mans run great on these settings too. Before I turned my settings down 25-mans were laggy and 40-mans were almost unplayable; I had to trust the tanks and healers were doing their jobs while I spammed hits. Wintergrasp battles were not playable but I haven't done WG in a while and I can't remember if that was before or after I adjusted the settings. Thankfully I don't have a set of pvp gear (yet!) so WG isn't a huge deal to me.
A previous post said they play at high settings and it runs great but I can't imagine that works in Dalaran, IMO.
One thing that has happened a couple of times is when I go back to windowed mode, so I could fire up Safari, iTunes, etc-, when I go back to WoW the graphics were EXTREMELY laggy for a while. A couple times I had to restart WoW to fix it. I suppose this is from the shared memory but I'm not sure.
Another thing, WoW makes my Mini quite warm and I would go so far to say it is borderline "hot". WoW is my only app that does this; everything else like iPhoto is fine. I would have to think that other games would do the same thing, especially given that WoW is fairly low on graphics requirements. To help out my little Mini I position a small fan, about 3-4" dia, so it blows down and across the top of the Mini. This works amazingly well and it's actually quite a cool looking fan. Only $6, too. It can be tilted to point straight down and originally I was going to put it on top of the Mini and have it blow straight down but the fan vibrates so I figured this would not be a great idea for the hard drive. Since I have a prop balancer, from messing with RC airplanes, I balanced the fan blade. I was able to get most of the vibration out of the fan but since it is a really cheap fan I could not get it perfect. So I plan to leave it along side the Mini until I upgrade the hard drive with a SSD which will be much more tolerant to vibration.
The SSD is planned but if I have to adjust my upgrade budget I will put in a Momentus XT. 4 or 8 GB of Ram is planned also. The memory upgrade may help the graphics too but I have not come across real data on that yet.
I hope my Mini experience is of help to you. Happy WoWing!
