The Kuadra uses kernel 2.6.10 (with updated kernel requirements), cyrus imap server, postfix mta, samba 3, samba vscan (virus detection on ibays), amavis-new, spamassasin, squid, squid-guard, openvpn, horde 3, mambo cms, etc. Most packages compiled from source.
Moses, you may have found already that SME7 includes Samba 3, Horde 3 and Spamassasin.
From what I've quickly read amavis-new can be integrated with clamd (which is what is in sme7), and improves the speed of virus scanning. So if you'd like to help with SME7, that may be a contribution you could offer to develop.
There is already an option I think in the latest SME7 Alphas to scan ibays, I don't think its samba-vscan, but likely accomplishes the same thing.
Regarding cyrus/postfix vs dovecot/qmail - I think it would take a lot of convincing for the developers to change that - they've just spent quite a bit of time better integrating qmail and improving its features. You may like what you see in SME7.
I am not really familiar with ACL - There was some discussion here a while ago about using Cyrus -
http://forums.contribs.org/index.php?topic=25261.0. For some it was an issue of needing shared mail folders. There is a feature in dovecot that is currently unused in SME I think, but it might be what you are looking for:
http://dovecot.org/pipermail/dovecot/2003-October/002497.html - I bet that could be integrated somehow in the server-manager of SME7
There is also an effort to create an Open-xchange add-on for SME7 -
http://forums.contribs.org/index.php?topic=26873.0Regarding shared calendars - the Horde application Kronolith now does that - I am planning on packaging that into an rpm for SME7 soon.
Openvpn would also make an interesting addition to SME7 - There is a howto for openvpn on 6.x which you have likely seen:
http://sme.swerts-knudsen.com/howtos/howto_30.htm- but it is not neatly integrated or packaged in an rpm.
Anyways, we're getting a bit off-topic for this thread - hope to see you on the Sourceforge mailing list and we can discuss any of this more.