> No, it's not great.  But there aren't great solutions here, unless 
> there's a thorough archive of many different versions of many packages.
> And it's even worse than I've just outlined, since you'll often find 
> that something doesn't rebuild properly.

I've been looking at how some of the other BSD's handle this, and
pkgsrc (especially when augmented with pkgdepgraph and pkg_chk) is way
above the competition.

I found that updating the pkgsrc tree to -current and then using
"lintpkgsrc -i" to find the out of date pkgs and updating with
pkgdepgraph is the least painful way to go.  Pain is relative though
and if something fundamental like png changes, expect 10-20 hours of
an unusable system with only the core non-pkgs utilities.

    set -e
    cd /usr/pkgsrc
    cvs -dAP
    lintpkgsrc -omr
    lintpkgsrc -i > pkgdepgraph.in
    pkgdepgraph -D pkgdepgraph.in > delete_order
    pkgdepgraph -R pkgdepgraph.in > rebuild.sh
    pkgdepgraph -F pkgdepgraph.in > fetch.sh
    sh fetch.sh && mv fetch.sh fetch.sh~
    pkg_delete `cat delete_order` && mv delete_order delete_order~
    sh rebuild.sh
    /bin/rm -f pkgdepgraph.in delete_order~ rebuild.sh fetch.sh~

Now on bad days, I may need to find what didn't rebuild, comment out
the broken build on rebuild.sh and rerun that by hand.  Still it beats 
rebuilding it all by hand.

-wolfgang