Supernet block sizes - recommendations?

I just had one of our customers turn in two class B addresses in exchange
for 130 C's. I'll make the trade,because it allows me to chunk the whole
CIDR block as a single entry, instead of two disconnected B's.

  Two observations:

  1. The NIC ought to take a stonger position to refer requests
     to folks with allocated CIDR blocks. I have had four sites
     turn in individual C's for numbers from our block.
  2. Once folks know this is possible, and works well, these numbers
     vanish. Perhaps this is only because we are working with
     state agencies who are building internal networks.