From previous posts I've read I believe that the official line is not to chew as it encourages your stomach to think it is going to get some food. If it's for breath freshening then Gold Spot spray is recommended.
Having said that, quite a lot of people do chew the gum with no problems.
I have a piece after my lunchtime bar - gets the bits out of my teeth and as I've just eaten my tummy won't be confused !!
I didn't really need the gum while I was on the diet. I spend alot of time chatting anyway so there wasn't time for it.(friends would rather put a brick in my mouth to shut me up) but thats their problem. I always advise a sugar free mint like the listerene disolvable ones. I dont know if it true, but I have been told on many occassions that if you chew gum you produce saliva which then stops the body burning fat as it thinks you will be swollening something. Makes sense to me but not sure if it is right. I have been told when chewing gum, mints etc that people do feel hungry so I do express this to people when they ask.