if you got greylisting installed, make sure to edit port 60000 to 10023 in main.cf in your postfix configuration.
dist-upgrading to mysql-server-5.1 will break the mysql server (temporarily)
MySQL will fail to start due to missing a few packages + old config simply wont work.
cp /etc/mysql/my.cnf /etc/mysql/my.cnf-5.0
cp /etc/mysql/my.cnf.dpkg-dist /etc/mysql/my.cnf
Then edit the new my.cnf accordingly after doing a dist-upgrade and upgrading mysql-server.