I'm in the audio industry, and we mostly laugh at the suckers who spend tons of money on Monster cable. There's a big psychological effect of those high dollar cables, though. I remember seeing a special 'audiophile' grade wall duplex receptacle being sold at a trade show a few years back. The thing was gold plated, extra low resistance, etc. The thing was being sold for more the $100!!!! Yet the wiring in most peoples houses is plain old romex spliced together with $.01 wirenuts. That's if you have a newer house. Most old houses have tons of receptacles linked together, with really nasty wiring. I bet that they sold tons of the $100 receptacles, though.
Audio-wise, it's a bit different in Pro-audio, since we use balanced cables to interconnect all our stuff, and nature of balanced audio reduces signal degredation. If you use decent quality audio and video cables, and steer away from the el-cheapo crap that comes with most pieces of gear, you'd be ok without having to take out a second mortgage to buy a set of Monster cables. We use 12/2 Belden 5000UE wiring to hook up all of our speakers, sometimes stepping up to 10 gauge for long runs. The Belden 5000UE costs us like 15 cents / foot. Maybe if you hooked up plain 12 gauge wiring and monster cable to an analyzer, you could detect a slight difference, but I can't ever remember any premium cable company doing that! Hmmm... why not!
We sell this fiber optic cabling that's really inexpensive, yet does a great job. The monster cable fiber was like $60+, and the stuff that I have was like $5 or less. Maybe it wouldn't work as well for everyone, but with digital, it usually works 100% or not at all.
Don't get me started about Bose!!!!