That's why I'm in favour to have a policy that permits allocations for specific, well-defined Anycast services. That allocations would come from a well-known block, so people would know to not filter /24s from there (and so on).
I agree that there should be a specific and well-defined policy. But I think that this policy does not need to be restricted to anycast services. It is a good thing to allocate only /24s and not any longer prefixes like /32 because there is no shortage of IPv4 address space and no need to conserve this space so severely. And I think that the well-known block used for this type of allocation should come from the old "Class C" swamp space. We have recovered lots of unused addresses from this area and we should begin to allocate them for special purposes which can benefit a large part of the community. --Michael Dillon