It depends on the person, but if your like me and on Atkins, its usually around 0-40. I stay well in around 25gms/day. REMEMBER - It takes less to get you into Ketosis, than it takes it keep you in. HOWEVER, there is a small thresh hold before you hit overkill and knock yourself out.
Also, watch your protein intake. To much will knock you out of Ketosis. It usually takes about 3 days to get into Ketosis. You have to process all of the ecess carbs, and let your body stabilize blood sugar first.