blocking resolving for 10.X.X.X addresses

[Simon Waters]

Steve Foster wrote:
> 
> we have found customers trying to resolv 10.X.X.X addresses ( or any other
> private addresses), i want to block these so they just get a "refused" or
> hostname etc.. not found...

I think more background is required.

Paul and friends have a project (http://as112.net/) that is
suppose to take care of this, and indeed is I do a "dig -x
10.1.1.1" I get NXDOMAIN, thats to the prisoner at IANA, and the
answer will presumably be negatively cached.

So what precisely is it about the current set up that has become
an issue? 
Or is there something else we should know?