I had my mikvah on a Wednesday or Thursday, so I just went to minyan that night as usual, but I told our chazzan, who had been asking occasionally whether or not they could count me, "Okay, so now you can count me in the minyan!"
A couple of weeks later I was given an aliyah, and my rabbi said a few words up on the bimah. Everyone was really happy and supportive, although a number of people said at the kiddush, "I had no idea you were a convert!" It was pretty funny, actually- I think of myself as being pretty open about the conversion thing, but I guess it just never really came up. I converted shortly before Pesach, so at a Seder at the house of some friends, I wound up doing the Four Questions, since I was "the youngest Jew at the table." Heh.