Ugh! Not this again! Tim Bray appears to be in favor of a scheme for reducing spam by having people pay a little bit for each bit of content they send or post that they want getting past the spam filters of the future. ongoing - Internet Stamps. Since such a system would require some sort of signing mechanism, and will require recipients to authenticate signatures of what they receive for it to be useful, why not use a free signing scheme? There are already some out there, and new variants could be created if they existing one's aren't sufficient.
On the one hand, I'm comforted by the fact that signing technologies aren't widely used (the exception being secure HTTP), because that suggests that nobody will want to bother to "up"grade their systems to support something like this. On the other hand, I'm terrified by the thought that if somebody thinks they can make money off of it, they just might be motivated enough to make it happen, and then we'll all be stuck paying them for something that should be free.