> One more question.
> When moving among the 3* versions (e.g. upgrading from 3.0 to 3.1)
> is there any benefit to rebuild packages?

There are two completely separate issues:

  A) Should packages be rebuilt because the OS has been upgraded?

  B) Should packages be rebuilt because pkgsrc has newer versions and
     bugfixes?

For an update from 3.0 to 3.1, or along netbsd-3, the answer to A is
basically no.  You might want to rebuild because of B, though, and I
tend to do a full update pass on a machine, updating kernel/userland and
then packages.  But when doing this along a branch, I only rebuild
out-of-date pacakges and those made dirty by 'make replace', not
everything.

My workstation has packages going back to 2005-12.  It was running
current, but I am not tracking netbsd-4.  Perhaps I should rebuild all,
but this is an example of how it doesn't hurt not to do so.