Yes, I have the exact same problem in the exact same spot (below the SteelSeries logo), though not as huge yet (9 months of use). I sweat a LOT.
They really should ditch these Omron micro-switches though. I've had double clicking issues in THREE buttons so far (left, right, and middle buttons).
I've managed to fix the left and right buttons by disassembling the mouse, opening the micro-switch and manually fixing them
The first one to fail, the left button, failed within 3 months from purchase (I couldn't return it because a friend brought it to me from Paris).
I'm unable to fix the middle button because it's too hard to remove the scroll wheel from it's place.
Very disappointed with SteelSeries.
Though it's a fact that most high-end mice use Omron micro-switches, I really have no idea why they keep using this POS...
EDIT: For your viewing displeasure, here it is:Edited by vittau - 11/22/12 at 4:17pm