Unless I am mistaken, the jump from 3.0 to 3.1 has some major configuration changes that will require a config audit to get figured out. Please correct me if I'm wrong on that version number though. For the most part, watching your syslog output will tell you everything that you need to identify and fix. Testing is highly recommended.
Absolutely. After applying some due dilligence, my upgrade went very smoothly. More information on these locations: http://lists.debian.org/debian-volatile-announce/debian-volatile-announce-2005/msg00011.html http://lists.debian.org/debian-volatile/2005/12/msg00013.html http://mail-archives.apache.org/mod_mbox/spamassassin-announce/200509.mbox/%3c20050914235232.814A45900BA@radish.jmason.org%3e
The v311 and 312 releases have very little/no configuration change requirements for upgrade.
As well as 313.