First up, im actually dealing with 2 as the 3rd clearly has no clue (Which he himself admitted before getting booted). And im DEBATING, as Pluto seems to be also 
On mains ~ Its a given that the CAT 5 cables in ethernet are twisted to counteract electromagnetic interference and preventing 'crosstalk'. THIS is a fact. As it stands I dont actually use a mains CONDITIONER. Rather ALL my cables (and my powerblock) are wired with braided cable. Now I know its hard for you to concieve John but the fact is its made a HUGH improvement upon my hifi and tv. Ive tried various cores and found that the 16 core I use straight to my powerblock in fact had the largest effect of all which sort of proves the theory that the more wires there are to 'cancel out' mains and electromagnetic interference the better the cable work. Im sorry but that is ALSO fact. My hearing is very acute and my eyes are virtually as good as you can get (for now).
Also, I lent my mate a Taacima mains conditioner and some silver braided cable for his tv (which looked cr*p on freeview in particular). I calibrated it but the horrible freeview 'blockyness' was still there.I left the cables with him a amonth and came back and the picture was CLEARLY better, most of the horrible 'blocking' effect had all but dissappeared! This was just after 1 month. My mate is 'very' happy (And didnt believe they would make a difference like you say) and has since bought a tacima and some braided cable for himself (And a PS3 as his dvd player was absolute s*ite)
You can quote as much as you possibly want to me but ive done all this here in my home. If you have some other explanation (OTHER than some placebo effect which you think can somehow fool me .....'forever'??) im all ears. But as it stands I really dont think you can. Do you REALLY believe that the very best electronics will work their best as the electricity supply jumps all over the place? (For the record, my supply isnt the greatest). Do you not think they will work best if the mains supply is as stable as possible?
My only explanation for absolutely refusing to believe what I say is that you HAVNT tried them for yourself (I think thats a given) and perhaps your eyes and ears arent what they used to be? Im sorry John but as people get older they 'tend' to slowly lose their sight and sound senses a little (thats ALSO a fact).
Even Pluto has stated that (When talking about speaker cable) the cable is chosen to TUNE the rest of the hifi system (Or to keep things as natural as possible dependent on what your trying to achieve).
Take my amp. I have an arcam A85+ which is still regarded as one of the finest sub £1000 players ever created (By some). Whilst not everyone would agree it IS a mighty fine amp. I actually had it connected via the freebie lead for 3 whole years (thats a guess) before I ventured out into the world of actually testing cables as I too didnt believe mains cables could make a difference. The very first cable I connected to the amp to 'test' was an isotek elite and the bass INSTANTLY sprang to life. And I truly mean instantly. I put a track on that id just been playing with the normal 'kettle lead' just minutes before and the effect was an instantaneous change. Thats not a placebo effect, thats FACT. And the reason I started looking into various cables and their effects. Its ALSO a 'FACT' that silver is a better conductor than copper (I have the papers on that somewhere). Now I didnt believe that silver would make a difference either as of course all the cables down the road to my house and the houses own wiring are all inherantly copper. Well im sorry, they make the biggest difference of all. Why? I really couldn't say, but I do have theories on it.
