I was actually pretty fortunate to have such an effective test system for comparing hard drive temperatures.  I am currently running a pair of Maxtor ATA133 7200 RPM 40GB drives in a RAID0 configuration.  This is an excellent scenario, because the drives are absolutely identical, and I was able to get temperature readings from both drives simultaneously.  They should both produce the exact same amount of heat as well.

I went ahead and applied the thermistors to the backs of each hard drive, directly in the center of the drive.  I didn't want to put them on top, because there is a fan blowing over one of them which would disrupt  the testing variables.  This method should give a pretty accurate drive temperature reading.

Unlike CPU's and Video Cards, hard drives are not required to run at any sort of working levels to get their temperatures high.  As long as the PC doesn't go into standby mode, or power saving mode shutting off the hard drives, they will always spin at 7200 RPM.  Therefore, I simply ran the PC like normal for a few hours, and waited for the temperatures to settle down.  Here are the results:

The reading on the left is the drive on which the Hardcano II is installed.  The reading on the right is for the identical drive installed in a regular 3.5" bay.  No other 3.5" peripherals were installed.

To test the effectiveness of the puny little fan (it pretty much makes almost no noise whatsoever), I also ran the system with it turned off.  After another hour of use, the Hardcano-installed hard drive rose in temperature by about 6-7 degrees!.  I am actually quite surprised that this puny little fan did anything for the temperatures, but you can clearly see that it did offer a major benefit.  The combination of the drive being installed by itself near the top of the case, and the quite little fan work together seems to have given us a nice measurable drop in drive temperature.  Good job!