An excellent idea, and something I've expressed some interest in before myself. Here's my $0.02.

My system is in a bit of a transition at the moment, since I'm experimenting with some different cables and trying to pick up some particularly nice stuff as the opportunity (and wallet) allow. Like Owl's_Warder, I was intrigued by all the talk about TMC's cables. A little persistence on Audiogon has allowed me to pick up a couple sets of TMC cables at a nice price. I've got TMC Yellow and TMC White going to my Model 750 (Whites on the surrounds; I intend to upgrade to Yellow there). I've got a TMC Yellow on my digital coax from a Panasonic A310 to my Model 1050 -- for this, I don't see much difference between TMC White and TMC Yellow (the Yellow is still burning in right now, so I can't say for sure yet), but the TMC White was noticeably different from the other digital cables I've used (Monster optical, Monster coax, BetterCables optical, BetterCables coax -- all of which sounded almost identical). I played with Monster, BetterCables, and TMC White on my VCR (fiancee watches TV from the digital cable box through it a lot): the BetterCables was a bit of an improvement over Monster, and the White was an improvement over the BetterCables (sound stage and sound floor). I've used several interconnects on my CD changer (all burned in at the time they were compared) -- Monster, TMC White, TMC Yellow, and a pair of Magnan Type Vi's that were loaned to me. I had interesting results here: the Type Vi's (retail around $600 or so) were an amazing improvement over the Monster Interlink 400 Mk II's, the TMC Whites didn't fair well when compared to the Type Vi's (they had a "weaker" sound than the Magnans), but the TMC Yellows actually sounded better than the Magnans on my system (somewhat less bass until I cranked it up at which point they were equals, but more and clearer mids and treble, somewhat better sound stage, and the dead silent background a lot of people observe in TMC cables) -- it was not an earthshattering difference, but I liked the sound more. I've got the Magnans on the CD changer until I can get my hands on a pair of Yellows for it. I am very interesting in doing a test of the Outlaw PDA cables. When they are available, I'll be getting a pair to test, and will probably compare them to TMC White and Yellow on my CD changer. I'll report my findings here for anyone interested.

For video, I've switched over to BetterCables S-video entirely. I have been fortunate in not having any problems with the S-video switching in my 1050, and have BetterCables older "premium" S-video from digital cable to VCR and VCR to receiver as well as the new Silver Serpent S-video from DVD to receiver and receiver to TV. I have found them to be better than the Monster S-video cables available at Best Buy, although they aren't as convenient and are slightly more expensive (~$50 or $60 for a 1-meter cable, I think). In fact, the change was immediately apparent when I used them in the DVD signal path -- better contract, richer color. I didn't see as much benefit when using them on the VCR.

I got very lucky with speaker cable this spring, while studying for the Professional Engineer exam. My future father-in-law gave my fiancee an old pair of his speaker cables, suggesting that she "loan" them to me. A pair of 2-meter Transparent MusicWave Supers, plus a set of jumper wires for the bi-wire binding posts on my Paradigm Studio 60's. I went from Home Depot 12ga biwired to the Transparents. Talk about an eye-opener! I've got the center channel biwired with BetterCables, although I've also used some old Monster M.75 (which bears a strong resemblance to a gray garden hose -- heavy stuff); both performed similarly. Trying either as the high-frequency in a bi-wire arrangement with the Transparent was comical/disastrous -- the Transparent was too much for them. I'm thinking about trying to get a pair of TMC Gold speaker cables to use as high frequency with the Transparents or as bi-wire for the center channel; if I do, I'll post my findings here. Lastly, my three surround speakers are wired with 30' to 40' runs of Monster XP white speaker cable.

My system (since a lot of this is system dependent):
Outlaw Audio Model 1050 receiver
Outlaw Audio Model 750 amp
Paradigm Reference Studio 60 v2 main speakers
Paradigm Reference Studio CC v2 center
(3) Paradigm Reference Studio ADP v2 surrounds
Panasonic DVD-A310 DVD player
Mitsubishi CS-27309 27" TV
Panasonic S-VHS VCR
Time Warner digital cable