It is not really possible to dispute this problem anymore. This is far too widespread, massively reported, and I (a huge supporter of Apple) have the same problem. If you don't believe how widespread this is, have a look around (away from macrumors?).
The thread on apple's support/discussion/ipod touch about this has over 20k views, and that's just one thread about this, there are plenty of others.
Just for reference, this is the problem in all it's glory...
http://home.comcast.net/~audi-fan/IMG_5940.jpg
here is also a good comparison with the iphone...
http://www.apple-touch.com/ipod-touch-screen-problem-negative-black-effect-1534.php
I did a side by side (with an iphone) with this video (which is a pretty good reference)...
http://youtube.com/watch?v=gyP8kEiHKxA
Now some people have been reporting that sometimes the problem (the negative, looks like you are looking at a screen wearing 3-d glasses thing) is there, then all of a sudden, they are somewhere else... and it's gone. So I tried out different situations...
We did the test by the window at my work (lots of natural light coming in), and presto!, the negative effect was gone! When just last night in a much darker situation (at my house) this scene was absolutely unbearable with the 3-d negative thing. Granted, the iphone still looked way better. My blacks washed into an ocean of blackness where all detail was gone while on the iphone i could totally make out the scenes. But I will go on record saying that there does seem to be an issue with the lighting of the room.
The worst thing about this is that people are going to the apple store under bright lights and these mighty apple folk are like 'i don't see much of a problem'... when there really is a problem.
Anyway, there is a real problem. I don't want to have to be in the perfect light at the perfect angle to view a product doing what it was designed to do.
Those of you with no problem, try it out in a darker situation, hopefully you'll still be all good, but... you never know.
p.s. - adjusting the brightness does nothing