Some interesting links:

ABX test results for various things (DACs, interconnects, speaker wires, scroll to table at bottom of page:

http://users.htdconnect.com/~djcarlst/abx_data.htm

Notice that no significant differences between any tested interconnects or speaker wires. However, a level difference of only 0.3dB was identifiable 76% of the time, up to 93% for 0.4dB.
Also interesting were the video and MiniDisc tests. In both cases, test tones/signals were different, but real-world material did not show identifiable differences.
This shows how our brains can tend to fill in gaps and hide things: basically the process that all lossy compression schemes (MPEG, DD, DTS, etc) all feed on.

Cable manufacturer won't do listening test:
http://www.vxm.com/21R.64.html

Will post other interesting finds later..