It all depends on what trade your going for. Obviously im no expert but I think for afew trades all the applicants go into a sift, and for some, only the weaker applicants go into a sift to compete for the left over places. If your trade is not recruiting at the moment then you will go into a sift so that they can discuss whether or not its worth giving you one of the future places. I know people who have been given a straight yes for Pilot who have the same scores as people who are in the sift for Int. I also know of people who have got a 3+ but got rejected befor the sift and people who got in after the sift on a 3-. The best thing to do is not to worry, you can't control it!
Oh, and, I rang OASC yesterday and the sift is expected to be late this month and we should have heard by early Feb!