I wear mine all the time when I run. Guess I'd never thought about sweat being an issue (given that it has a little clip and all, that's kinda what it's *for*). Anyway, I guess I'll quit clipping it to my sports bra and find somewhere a little drier.. guess that also means that when my shuffle battery dies I probably shouldn't be tucking my 80gig classic into the back of my waistband either.