Any network provider which is using multiple ANS/NSFNET connections to split load should have an addressing plan that assigns a different aggregate to each exit point. The basic rule is: for each routing policy you have, you should have different CIDR block. I thought we'd been over this in at least the Regional Techs forum before.
Unfortunately, PREPnet already has a CIDR block half allocated, and it doesn't match the policy needed to do traffic splitting into ANSnet. It would be wise to do this, but only when you can foresee what the policies will be in advance. If you can't guess what your policy will be in the future...
Another future happy customer of Dennis's route coloring. Either that or we could make some configs that block announcements of IBGP refines of certain aggregates. More work for Dale and friends. Boy do we have job security! Curtis