Update to 9.2.1 had some minor problems for me. The updater had to run twice and took long time because of the checking of all mailaccounts (>1200) on the server (first update with spammassassin, second with drweb). First Update took about 45 Min. - in this time apache was down and dns not ok. After this, the second update stopped qmail/xinetd, no telnet on port 25 possible for further 45 minutes. After this time, all went automaticly back to be ok. But in these 90 minutes, i thougt "oh no, no more plesk-updates".
At the moment, all seems to be fine.
Will start testing greylisting with qmail the next days, but not sure about that because of some posts about high cpuload with greeylisting...