We have assigned 'chunks' of old-style B's in cases where
it made a significant difference (obsolete equipment).
Again, I see no technical reason not to do this;
as far as your routers are concerned, there is not difference
between 191.191.0.0/18 and 194.194.0.0/18
Geert Jan
(trying not to get into the discussion of the validity of
prefix length filtering again)