You can easily tell the diference between 16 bit and 32 bit colour, but only because with 16 bit you can see graduations on lights and sky textures. With 32 bit they are all smoothed out.
I very much doubt that 128bit will be noticable over 32bit, certainly to to any great extent.
This sounds like an excuse to sell us more expensive memory than we need. Making high polygon games is expensive to develop. Making 128bit couour games will be less expensive and just as demanding on graphics cards.
Im running a GF3 thats over a year old and I can still run any game at 1280x1024 resolution, I have no need to buy a GF4 and I will probably be able to keep this card running (once volt modded and
OC) untill the GF6 is out. Nvidia and others need an excuse to sell us another card as current games just arnt demanding enough.