I'm playing around with pkg_check -u and make update in pkgsrc.

  I've observed that "make update" runs pkg_delete -r, then builds the
  package, then re-installs the dependencies.

'make replace' rebuilds the packet out from under the dependencies.
This often works, but will lose if the shared library versions change.
In that case, you can do make update.

More complex schemes to get efficiency without losing safety have been
talked about, but not yet written.

-- 
        Greg Troxel <gdt@ir.bbn.com>