Is there actually a difference?

There are so many variables that can screw up such a test. The speakers being a big issue. Some speakers are dark, dark speakers will hid variations. If you find a good full range driver, you have no crossover issues, and assuming that the speakers are articulate, these should make it easier to identify differences in equipment assuming that the high end gear is truly articulate, expensive equipment doesn't guarantee that the equipment is articulate or neutral, it only guarantees that it'll cost a lot. In my system non audiophiles can consistantly identify different gear, be it amplifiers, most cables, etc. Mind you, they don't always prefer the better (more neutral) items. Just as some audiophiles prefer dark sound some neutral, and some prefer bright equipment. I'm sure that some people couldn't tell any differences, but I haven't found anyone who didn't hear changed, when there actually was a chance. Then again, I use Teflon V-Caps, or Russian caps, Mundorf Silver Gold Supremes, and even particular resistors, so my system is tweaked to the max. Only my Yggdrasil is stock.

In my opinion, it would be VERY easy to set up a double blind test where people would be unable to hear differences in various equipment. I would love to find a skeptic to work with where I pick the speakers, and the high end equipment. The speakers I would use would be 8 ohm, and over 90DB at 1 meter, not a difficult load, and very efficient. The difficulty comes into play with the DOUBLE blind part. Switching between 2 systems, level matching them, keeping the testers in the dark, and being able to immediately switch back and forth between gear so as to assist people in hearing differences would be the most difficult part. Anything truly random could have you listening to the same system after hitting the random selector switch 20 times before hearing the other system. I think a double blind start, and then allowing the listeners to swap systems at will would make far more sense. Honestly though I have strong suspicions that the naysayers have been allowed sufficient free reign to allow them to game the system. I think that the most important part of the test would be ensuring that the speakers are extremely articulate. I believe that there are many speakers out there that would easily mask differences. Other announces such as acoustically lively rooms, as in tiled floors, or excessively dead rooms, as in rooms with heavy carpet, and foamed walls could have an effect. I am not a room treatment guy, I figure music is played in imperfect rooms, but I do believe that in a double blind test too hot or too dead a room could color the results. I'd really like to be involved in one of these tests before ascribing any merit to them. I think that they could too easily be rigged otherwise. 

Dave_b, taking time to get a handle on a system's sound isn't the same as being able to hear differences. Before you take a hearing test, you are supposed to have had 8 hours of only low level noise, that can impact an A/B test. OTOH, if someone can't tell the difference between my amp and preamp, given a very good source, and articulate speakers, something is wrong with their hearing. To know what my system does well and does poorly would require more extensive listening, IMHO. I could be wrong, but my experience says otherwise.

Dave_b, only that when doing an A/B particularly with consumer vs transparent articulate equipment, listeners ought to be able to identify each, though which they prefer would be a matter of taste. As for us, when we do something to our system it's often a small tweak, and it can take us an extended period in order to fully grasp its total effect. Often we can immediately hear a difference, but some components need to burn in, and even if not, it's often not immediately obvious the extent of the changes. So in one context I agree completely, but if you were referring to an A/B with consumer quality gear, and truly high end gear, then I disagree.