I put mine in my pocket when using my exercise bike and it logs more steps than when I wear it on my wrist, so yes I think it's OK. I haven't checked how accurate it is, though, although that would be easy enough to do. (Set the timer, count 100 steps say, stop the timer and see how many steps your Jawbone has logged when it's in your pocket)

I spend a lot of my day pushing a pram or carrying a baby around and not swinging my arms, so I put mine in my pocket, or hook it through belt loops or even my bra sometimes. It still registers the steps for me.