Next to nothing, it is a switching regulator probably has about 80% efficiency. As the gps draws about 1.2W (240ma at 5V), it is probably in the order of 0.3W. I mounted it inside the same aluminum box as the receiver, and the box gets warmer on the gps side than on the max233/pt5101 side.
It doesn't need an additional heatsink even when you draw a full amp at 5V.