[rosser]

I've also used exercise balls for a couple years now -- at home, and at the former office. You'll find that your core muscles (abdominal, in particular) tone up significantly, with almost no apparent effort. The inherent instability of sitting on what's essentially a balloon benefits more than just your posture. All those small adjustments you unconsciously make to maintain balance work muscles that you don't often get to work otherwise, and with a wider range of motion than pretty much all the traditional exercises that target those muscles offer, too. It's some of the best "passive exercise" available.

As for the concerns about being made fun of or judged or whatever, mentioned several places in this discussion, someone's judging you says more about them than it does you.

And, yes, they do tend to have a resonant effect on certain reverberative sounds...