portupgrade and freebsd-update: A better way?

[Peter Beckman]

So I took on binary upgrading one of my FreeBSD servers today from
6.2-RELEASE to 7.0-RELEASE.  Many useful sites outline exactly how to do
this right, and they are mostly useful.

Except when it comes to ports.

     http://www.daemonology.net/blog/2007-11-11-freebsd-major-version-upgrade.html
     http://www.cyberciti.biz/faq/howto-freebsd-server-upgrades/

You get a few production servers with 200+ ports installed, and upgrading
could take several days and lots of headaches and a lot of babysitting.

Is there some sort of automated way that someone smart has figured out how
to determine which ports are actually affected by the upgrade, so I only
have to upgrade a hopefully small subset of installed ports?  Are ALL the
libraries upgraded during the OS upgrade modified in a way that breaks ALL
existing ports?  My gut says no, but my brain says it's not trivial to
match the two together to limit the number of times you have to rebuild a
port.

Is there a better way?  Does portsnap or portmanager or portupgrade keep
track?  What have I missed?

Beckman
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Peter Beckman                                                  Internet Guy
beckman at angryox.com                                 http://www.angryox.com/
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