My doc uses one each and every visit. I haven't bought one although I have been guilty of using my stethescope to listen to baby movements (not heart beat). Most of the time I don't even think about it - I even get surprised when I go to the doc and she does it - even though she does it ever visit! But if I'm bored or avoiding study.... out comes the stethescope!
*if* i were going to buy one though, I would rent one first and see if I liked it before forking out the money to purchase one. I'd definatly get one off EBay...

HTH

MG