Upgrading pkgsrc; a summarized discussion

Siju George asked about updating pkgsrc packages, both on DragonFly mailing lists and on pkgsrc-users@.  The ensuing discussion can be boiled down to several alternatives: pkg_chk in a separate chroot, pkg_rolling-replace, or pkgin, pointed at avalon.dragonflybsd.org.  I’ve used pkg_rolling-replace several times with good results, and it may be possible to convince it to use binary packages, too.