Ecole Centrale de Marseille
2 Servers: 2x Xeon(R)5130 @ 2.00GHz (active/passive)
OS: FreeBSD 7.1
RAM: 4 Gb
Users: 1600+, ~160 simultaneously active.
Authentication: OpenLDAP + pam/pam_CAS for webmail
Storage: Maildir on a NetApp via NFS, with RPC (filesystem) quotas
Users Maildir Size: 2700MB per user (at least)
Dovecot version: recent 1.1
Client Software: webmail (dimp/ingo from Horde), Thunderbird and some others (IMAP/ssl only, no POP here)
Only one server is working at a time for dovecot and postfix (delivering up to 500 msgs/minute via deliver)
amavis + virus scanners (scanning up to 600 msgs/minute) is load-balanced on the same 2 servers
Sample load of the 'working' server this week:
Number of 'imap' processes (8 of may is not worked here 
We are using dovecot since 2006 (1.0, then 1.1 versions of dovecot, RPC quotas working since 1.1) for:
deliver
postfix SASL authentication via auth-master
IMAP service of course
managesieve (Client: Ingo (Horde project)