The common thread here seems to be multiple monitors. I do not have any of the conditions lordloki described. I have two installations, one is a 64 bit installation that is a continual upgrade from Vista (Vista --> 7 beta 7000 --> build 7022 --> 7048 --> 7057) and the other is a fresh installation of 7057 32 bit. Both of them doing exactly the same thing all of us are experiencing.
I wonder this: Do all of us have multiple monitors with multiple resolutions? Perhaps a vertical resolution setting on one monitor is somehow influencing the other monitor, but only for icon placement? Follow me here, my secondary monitor is 1680x1050, but my primary monitor is 1024x768. Is it possible that the boundaries for the icons on my primary monitor is vertically set at 1680 (or something like that)? Just a shot in the dark, but something worth playing with. THis is obviously a bug of some sort.
My video card is an ATI 4850, so it's evidently not card specific, either.