In an effort to gauge the efficiency of the Neptune's massive cooling system, I used Everest Ultimate to log temperatures in 5 second intervals while loading the CPU with Prime95.  The results are below.

If the graph is not clear, I do apologize.  Welcome to the special hell that is graphing with Excel.  The idea here is to show CPU load versus core temperature over the span of about 30 minutes, and to see how fast the system removes the heat.  The dark blue lines in front are the 8 logical cores of the Core i7 965 CPU and the light green and light orange in back are the measured core temperatures.  We can see a nice correlation between CPU load and CPU temperature.  The darkish green is the motherboard temperature, and the darker orange is the CPU temperature (package temperature, not core temperature).  Package temperature is the same the cores, only 20 C cooler.

The First thing to notice here is that at 4 GHz, the 965 is being pushing to a rather uncomfortable 82C at full load.  While we enjoy hot game on CPU action, this is a little too much.  We did at least have the thermal protection enabled.  The first blip is where I started Prime95 in the first place, as well as CPUZ and Paint.net to capture screenshots.  The other noise at the end of the graph is where I did all the review stuff one needs to do.  Now the very impressive result is that the Neptune's water cooling system dropped from 82C load to 41C idle in less than 5 seconds. This is very good performance.

A small aside, notice that this particular chip has two 'hot' cores, which are about 2-4 C higher than the other two cores.  There's nothing to do about that, it is just the way this CPU is made.  However, we feel that the DangerDen MC-TDX could be a little better at sucking up the heat, though, since the GTX480 radiator is more than capable of absorbing the nearly insignificant 130W of this CPU.  Something like a Swiftech Apogee GTZ might offer better performance.  But, ah, it probably wouldn't look as good :)

Here's a screenshot of the test itself:

Everest HD Test

Everest Ultimate has a built in HDD test, which we were happy to use, since HD Tach doesn't yet run on 64-bit Vista.  It did provide some impressive and thorough numbers, however.
 

There isn't any doubt that two VelociRaptors in RAID0 is fast.   The average read speed is just about 200MB/s, which is very fast.  Of course the RAID 1 numbers below are paltry compared, but with big storage speed is not the issue.  I tend to disbelieve the 0%CPU though, but you never know.  So, this isn't SSD speeds (about 220-250MB/s) but it's not very far off and costs a chunk less money for a lot more space.  It is becoming popular to see SSD for boot drives these days, but of course the cost is still very high and the write speeds are not as good for the cheaper SSDs.  So, I think there's still life yet in mechanical hard drives.
 

Noise
I was rather unlucky in finding an SPL meter, but several pair of ears confirm:  Loud.  Honestly. Close to 60dBA.  If I understand correctly, the Black Ice GTX480 radiator in the Neptune works best with a lot of fan.  Thus, a lot of fan equals a lot of noise.

Smell
It does not smell like fish tank, in case you were wondering ;)
 

GPU Overclocking.

Whoah, nelly.  I was able to get 756MHz out of the GTX280 video cards easily (with according shader domain clocks), which is pretty amazing.  The cooling system did a kick-ass job here, the cards never got above 45 C, if you can believe that.
 

 3DMark Vantage with GPU overclock

Far Cry 2 with GPU overclock

In both Far Cry 2 (DX10) and 3DMark, just overclocking the video cards has a decent gain of more than 10%.  Obviously, very playable.  It might make a difference at the highest resolutions (1920x1080 and up), but even at Ultra-High settings, the Neptune won't be letting you down in terms of playable IQ.

As you see, this machine is very fast.  It's the fastest PC I've ever used.