The whole idea is to remove exess weight that isn't doing anything, not to drill holes in, say, your cranks. You'd be very, VERY lucky to get half a kilo. I drilled all round the sidewalls in my front rim and saved 18g, and you have to find 500g. Your talking cutting off the bash plate mounts wich is about 15g, hole in the head tube which is about 10g. (Estimated weights from memory). Everyone breaks stuff in trials, but in my experience, it's the street riders that go really big that snap stuff all the time. I prefer to ride natural and comps, so my bike doesn't get hammered, so it can be weaker. The whole point is to conserve stregnth whilst loosing weight, which is why you don't do massive holes in the headtube or bb, or make holes in the chainstays.