Yeah, a pair of needle-nose pliers worked for me too. Open them up and place the tip of both tines into the notehes on opposite sides. Apply downward pressure and turn. Beware: you likely will scratch up the back of the watch as the pliers will probably slip out a few times. But, if you are like me, you wear the back of your watch next to your skin where no one can see it.
I have another that I want to open as well, but it is being stubborn. Not giving up yet, however. Worst case, the local jewelry store should be able to get it open with no problem. I'll just ask them to open it, and do nothing more. They will probably do that for free. I can replace the battery myself...cheaper than they will.
Joe, June 2008