I think we're talking about filtering the 64.0.0.0/8 prefix, EXACT prefix.
That wouldn't block anyone from reaching anything as long as you only filter
the /8 and not any of the more specific advertisements.
My company's got a /16, a /17, and a /18 out of 64/8 and I *WANT* people to
filter out the annoying 64.0.0.0/8 prefix that much of my traffic may be
destined for if something explodes on my end and my routes get withdrawn.
Paul