I was just about to start one of these threads myself
This is the third Intel iMac I have owned and is hands down the most powerful iMac I have had to date.
I got the i7 because I have a server with approx 350+ movies on it (all still in TS format) and I want to change them all to .m4v to save space and play the movies on several different devices. Plus I have been waiting for the Nehalem class of processors since it was announced.
I opted for the 8GB of RAM and the 2TB HDD. I probably didn't really need the 8GB of RAM but when spending this much I really wanted to future proof it as much as I could.
I am currently using Handbrake to do the change. I generally queue up 10 movies and turn the i7 loose, on average the i7 chews through 10 movies in about 3 hours!!! That is turning an 8Gb TS file into a 1GB m4p file in about 20 minutes or less. At first I would set that up and leave it work. Then wanted to do more stuff so I started using the iMac as I normally would, having lots of apps open, editing some photos, music playing and burning movies to disc all while the video were encoding. I never noticed any thing slowing down at all. My 24" C2D 2.8 would take about an hour for 1 movie.
This i7 is very quiet, only detectable noise is the sound on the air moving through the chassis by the fans, not the fans, just the air moving. The optical drive is very quiet too, it is barely audible even when burning a disc at full speed. (much quieter than the one in the C2D)
The screen is not perfect, it does have the yellow tinge at the bottom. It is very slight and only noticeable when staring at the grey bars.jpg. I will wait to see it gets worse, if it does I will look at getting a replacement when the issue is fully resolved by Apple. And I have 1 stuck pixel in the menu bar of the screen. Even with that, the screen is incredible.
Overall I am very happy with this machine, but I was nervous before I received it because of all the negative things that I had been reading here.