Just recently updated my vps to ubuntu 11.10, this went mostly smooth. However, I had some issues with dovecot. I could not get it to start.
It seems that the configuration guide I followed to setup dovecot broke due to outdated settings. However thanks to a wiki guide from dovecot, I was able to convert my configuration file: http://wiki2.dovecot.org/Upgrading/2.0
However, dovecot refused to work properly. After much searching and much issues, I finally figured out that I had to install a new package, dovecot-mysql in order to get this to work. After which, a restart of the saslauthd service brought everything back into working order, at least for dovecot