I've been using Kerio Control for a long time, and I must say I have been generally very pleased with the product. Granted, it does have its faults, just like any other product (HTTP inspector instability, lack of IPv6 support), but I am very pleased with the inclusion of Snort.
I have a couple of issues that should be at least considered, though. They should be pretty easy to implement as well, since they aren't dramatic changes. I've been playing a lot with the distribution of Snort that comes with Kerio Control, and if I interpret things correctly, you are using nfq to handle packet capture. There is a bug in Snort (up until 2.9 IIRC in which the Unified2 logs are unparseable by Barnyard2 - it tends to throw a ton of "Not IPv4 Datagram!" error messages and discard all the packets. Hence, nothing can be logged to an external database for further analysis and reporting.
My suggestion as a stopgap (because perhaps compiling Snort 2.9 is problematic with all of the patches you've done? I'm not sure from looking at the source available from Kerio) is to just compile the snort you distribute with Kerio Control with MySQL support enabled as well. It wouldn't add any excess baggage to the memory footprint, per se, and give systems administrators a lot more flexibility in terms of logging and reporting of intrusions.
My second suggestion for Snort is in the snort.conf template file. You might want to consider moving to using "config detection: search-method ac-bnfa-q search-optimize" instead of "config detection: search-method lowmem". Lowmem is a much older method, and is lower performance than ac-bnfa (which is now the default these days). It does increase the memory footprint a bit, but also speeds up processing of traffic, which can make a noticeable impact on loaded networks.
P.S. And yes, another vote for IPv6 support. Where I am here in France, many ISPs now (and have for several years now) offered native, non-tunneled IPv6 support to clients. I know that retooling Kerio Control for IPv6 isn't exactly an easy task, but on the other hand, now that IPv6 Day has come and gone, it's becoming a very important issue.
EDIT: Support Ticket filed.
[Updated on: Fri, 17 June 2011 15:36]
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