Here's the output for my dovecot.conf file that works after I upgrade Ubuntu 10.04 to 12.04 Precise:

auth_default_realm = xxxxx.org
auth_mechanisms = plain login
dict {
  acl = mysql:/etc/dovecot/dovecot-share-folder.conf
  expire = db:/var/lib/dovecot/expire/expire.db
  quotadict = mysql:/etc/dovecot/dovecot-used-quota.conf
}
disable_plaintext_auth = no
first_valid_uid = 1001
last_valid_uid = 1001
listen = *
log_path = /var/log/dovecot.log
mail_gid = 1001
mail_location = maildir:/%Lh/Maildir/:INDEX=/%Lh/Maildir/
mail_uid = 1001
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
namespace {
  inbox = yes
  location =
  prefix =
  separator = /
  type = private
}
namespace {
  list = children
  location = maildir:/%%Lh/Maildir/:INDEX=/%%Lh/Maildir/Shared/%%u
  prefix = Shared/%%u/
  separator = /
  subscriptions = yes
  type = shared
}
passdb {
  args = /etc/dovecot/dovecot-ldap.conf
  driver = ldap
}
plugin {
  acl = vfile
  acl_shared_dict = proxy::acl
  auth_socket_path = /var/run/dovecot/auth-master
  autocreate = INBOX
  autocreate2 = Sent
  autocreate3 = Trash
  autocreate4 = Drafts
  autocreate5 = Junk
  autosubscribe = INBOX
  autosubscribe2 = Sent
  autosubscribe3 = Trash
  autosubscribe4 = Drafts
  autosubscribe5 = Junk
  expire = Trash 7 Trash/* 7 Junk 30
  expire_dict = proxy::expire
  quota = dict:user::proxy::quotadict
  quota_rule = *:storage=0
  quota_warning = storage=85%% /usr/local/bin/dovecot-quota-warning.sh 85
  quota_warning2 = storage=90%% /usr/local/bin/dovecot-quota-warning.sh 90
  quota_warning3 = storage=95%% /usr/local/bin/dovecot-quota-warning.sh 95
  sieve = /var/vmail/sieve/%Ld/%Ln/dovecot.sieve
  sieve_dir = /var/vmail/sieve/%Ld/%Ln/
}
protocols = pop3 imap
service auth {
  unix_listener /var/spool/postfix/dovecot-auth {
    group = postfix
    mode = 0666
    user = postfix
  }
  unix_listener auth-master {
    group = vmail
    mode = 0666
    user = vmail
  }
  user = vmail
}
ssl_ca = </etc/ssl/certs/gd_bundle.crt
ssl_cert = </etc/ssl/certs/imap.xxxx.org.crt
ssl_key = </etc/ssl/private/mail.server.key
userdb {
  args = /etc/dovecot/dovecot-ldap.conf
  driver = ldap
}
protocol lda {
  auth_socket_path = /var/run/dovecot/auth-master
  log_path = /var/log/sieve.log
  mail_plugins = quota sieve autocreate
  postmaster_address = root
}
protocol imap {
  imap_client_workarounds = tb-extra-mailbox-sep
  mail_plugins = quota imap_quota autocreate
}
protocol pop3 {
  mail_plugins = quota
  pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
  pop3_uidl_format = %08Xu%08Xv
}