has anyone done something like the above?

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My SwiftCarbon Ultravox

My Giant Defy Advanced

Not just yet... I was planning to though, I got a bargain BMX seat which already comes in at 170g, you can see in the link below that its ribbed design makes it easy to tell where the potentially drillable areas are. Of course the curvature of the seat itself can contribute to the strength and be integral to its structure. Ultimately I was going to start by trying one hole, see how much that amounts to in weight reduction and then decide whether it is worthwhile. Not exactly mega performance stuff though!

http://www.ebay.co.uk/itm/200806595965? ... 1497.l2649