Just got back from Candolim, I didnt get one bite and neither did my OH, we didnt take malaria tablets but I would not encourage anybody else not to take them, saw very few people with mossie bites but they are out there, I just used mosquito repellant with 50% deet which I find very very effective and would not use anything else( can be purchased from Boots but is expensive you need about 2-3 sprays for a 2 week holiday), I know you can purchase repellant in Goa but I find best to use what you know works.
On the down side one of the maids at our guest house came down with Malaria so be aware...
Steve