Two biggest things are upgrades, both OS and packages.

OS - I build releases on freebsd6.cs - mount /usr/{src,obj} from freebsd6 to the local machine, then make installworld etc.

Packages - I'm experimenting with using pre-built packages from the FTP mirror site, rather than building everything I want on freebsd6. For this you need to make changes in (at least) two places.

/etc/make.conf:

MASTER_SITE_BACKUP?= \
http://mirror.cscf.uwaterloo.ca/pub/FreeBSD/ports/distfiles/${DIST_SUBDIR}/
MASTER_SITE_OVERRIDE?= ${MASTER_SITE_BACKUP}

should be added.

Add the following lines to root's .cshrc, and always use su - or sudo -i:

setenv PACKAGEROOT http://freebsd-mirror.cscf.uwaterloo.ca
setenv PACKAGESITE http://freebsd-mirror.cscf.uwaterloo.ca/pub/FreeBSD/ports/packages/Latest/

After that, pkg_add -r or portupgrade -PP should work as expected.