Rob Thomas wrote: The reality is that the miscreants are seeing a lower return on the investment when spoofing from bogon prefixes.

Because they are being filtered :-) If more people filtered bogons, the "ROI" would be even lower. Although it is clear that bogon filtering is not a complete cure for spoofing, it does help and it also helps for some spammers. The only negative effect of bogon filtering is not-up-to-date filters, which is why we have written this draft that will expand the applicability domain of bogon route servers and other filtering schemes. Michel.