I've finally found the time last time to look into the problem Adium had to connect to DJabberd using DIGEST-MD5 of SASL.
I wasted some time at first because, by default the trunk in subversion builds libpurple with cyrus-sasl which is immune to that problem, so I had to disable it to test the patches. Here are the patches:
http://pidgin.im/pipermail/devel/2009-January/007402.html
http://pidgin.im/pipermail/devel/2009-January/007409.html
Adium + cyrus-sasl can do auth-conf. Cool! I should test that (not really useful, as people should just do STARTTLS+PLAIN)
