Hmm...I've worn the G Watch every day since I got it. I sweat like crazy when at work, and definitely while I'm biking or hiking. It's been through ocean water, filthy pool and jacuzzi water, lotion, sunblock, and some food condiments. Have yet to see any discoloration or corrosion to the device or my arm. Maybe you guys are eating something funky.
I do sweat a lot with this watch though. It's probably the worst watch band I've ever worn. My wrist stinks at the end of the day.