weird BGP cisco-ism? [problem resolved]

  You can build your customer BGP filters off data in the IRR. Make
it a requirement that BGP customers must keep that information up to date
(or do it for them).

OK. So I apply an ingress filter (ideally built from the IRRs) to a customer
peer. Then I have to add the cusomter's AS(s) prefixes to every eBGP peer's
egress ACL (including customer peers) so that the networks will be permitted.

The customer begins advertising a newly allocated netblock. Now virtually
*every* BGP peers ACL has to be modified & deployed and the source AS will
need to either flap the route or reset the session.

If I had tagged the customer's prefixes with a BGP community when I picked up
the routes ..and have filters in place that deny/permit predefined communities
to all eBGP peers, all I would need to be concerned with is the customer's
ingress ACL.

IMO, ACLs alone won't scale.