In the referenced message, Roy said:
In a recent discussion with a company that owns a /16 and has it broken down further, the statement was made that there are ISPs that filter routes at /16 in what was traditional class B space. The example cited was Verio. Verio web pages state they don't do this any more (the filter is /21).
Is there anyone that still filters routes longer than /8 and /16 in the traditional Class A and B space?
Assume this is the case, announce your largest aggregates, and reduce the likelihood of ever having a problem in the first place. This does not prevent you from advertising additional more-specifics to entities who have agreed to accept them, nor does it prevent others from filtering them. In the end, you still have connectivity, and only those who wish to see the more-specifics, will.