I touched base with my accountant and asked him about what the rules were around charging GST as a contractor. The rules (according to the Canadian governments website) state that you only have to pay GST if you make $30K in one calendar quarter, or over 4 consecutive quarters. But I've heard some differing info from people about GST, and that you have to pay back the GST for that initial $30K once you hit that number.
So anyway, the government phone number for info kept giving me a busy signal, so I turned to my accountant for info. He said that basically once you hit 30k you have to register for GST and start charging.