I use these as well (the Backbeat 903's). However, I don't sweat wearing them, I take brisk walks, and bellydance.

I do love that these charge with the same charger as my phone. It means I can use a single car charger (I used a split charger when I had the Motorola S9-HD bluetooth because it used mini-USB).

The mic appears to be much more powerful on these (than the S9HD). When I talk hands-free in my car, people comment that they can hear my windshield wipers, engine sounds, etc. They can also hear me just fine.

They're so much lighter-feeling than the S9's. I didn't find the stiff bar around the back of my head "that" annoying, but it is nice to have it replaced with a flexible wire.

Looking at the way these are sealed, I don't really see anywhere that sweat would soak into the circuits. All the seams are closed with rubber (which I would expect would form a tighter seal than plastic).

So, I would say you could at least "risk it".