What were we saying about edge filtering?

Don't confuse the source and destination. This traffic is packets with an
unused DESTINATION address.

Ok, you got me there. I do wonder, however, how much is responses
to traffic that began life as an unused source.

There is still the point that the catch-all route is causing more
hauling of traffic than is necessary, and would prevent uRPF from being
able to do its job (presumably so that back-scatter based backtracking
could work, which would be unnecessary, if RPF were implemented.)

loose uRPF has *NO* effect on the destination address.

True enough, it has no direct effect. It might have indirect effect, however.

Which is greater in a typical backbone? Traffic with a bogon source, or
traffic with a bogon destination entering the backbone?

This is probably a function of how many customers are default routed
and how much the backbone filters.

If we make the assumptions that the larger backbones have primarily
BGP-speaking customers, and do relatively little filtering, then
I'ld say it would be primarily bogus sources.

As either the filtering or customers pointing default goes up, I'ld
expect the weighting to even out or swing towards more bogus destinations.

Thankfully, bogus destinations die when they reach the default-free zone.
The same is not true of bogus sources.