Jaeson,
While you have been delightfuly thorough with providing information related to your problem, you appear to have neglected to mention which version of Dovecot you are using. I'm sure the list would like to know.
I don't use SQL based user auth, so I can't help much there, though it all looks ok to me.
Finally, here is the configure command I used when building Dovecot from source:
./configure --prefix=/usr --enable-debug --with-pgsql --with-cyrus-sasl2 --with-ssl=openssl --sysconfdir=/etc
Why have you put "--with-cyrus-sasl2"? Last I heard that wasn't working, and even if it was, I've never heard good things about it. Dovecot has its own SASL implementation, which by most reports is very good.
At this point, I think that the connections to my postgresql tables are all working properly, and the initial authentication with Dovecot appears to be working. Dovecot *does* accept my password and gives me the "OK Logged in." response message, but somewhere before it kicks off the IMAP process it dies with a SIGSEGV. Perhaps I have some file permissions out of whack? Has anyone else encountered this problem, or perhaps has any insight into what might be going wrong or how to find out more information?
I do recall some messages on the list recently about recent patches unbreaking DB connections. Of course, this would depend on which version of Dovecot you are running.
-- Curtis Maloney