Hi Mike, we're both right. According to West http://www.westsystem.com/frames/tier2/usingepoxy/healthandsafety.htm it is the partially cured epoxy that poses a hazard. But, you don't get a full cure for two weeks. I think it's safe to say that most of us do sand uncured epoxy. Thank you for making that distinction. Here's my sensitization story:

My friend and I built two yaks several years ago. We weren't that careful glassing and got a fair amount of runs on our fill coats so we had lots of sanding. My friend got sensitized somewhere along the line (maybe because it was his house) and he developed a sore itchy rash on his forearms. The rash became inflamed every time he touched the sander. He was pretty uncomfortable for the rest of the project.

Be safe. Don't underestimate the hazard.