I upgraded my server to Debian 8 (jessie) tonight.
It went quite smoothly - I had to configure ejabberd again (they've changed the configuration file from Erlang to YAML), and I had to change the names of the files in Apache's sites-enabled/ directory to end in .conf, move the stuff in conf.d/, and switch from mod_gnutls - which is in oldstable and in unstable, but not in stable - to mod_ssl, but that was basically it!
pg_upgradecluster nicely did a dump/restore of my PostgreSQL databases, upgrading from 9.1 to 9.4.
Even rebooting the machine went without a hitch.
Well done, Debian!