Used it, liked it, but...
We started out with Citadel, then used Zentyal for most of our in house stuff, but there are a few things we didn't like. Eventually we found that we needed to replace Zentyal with a better, more integrated solution.
The first seems to be a common sin... putting an IPv4 firewall and proxy on the same application stack as the infrastructure. C'mon guys, at least virtualize it! Naturally you can disable the firewall part, but it's just begging to get a noob pwned.
The second issue I had with Zentyal is another style thing. If you are going to put the system in a rack and make all services administratable from a web interface would you spend the memory and clock cycles in putting a GUI on the distro? have a look at your Zentyal server's CPU load under no load, then drop the runlevel down to kill the GUI. On a P4 2GHz, I was spending half of my computer's time making pretty pictures for no one in particular, unless you count the elf who lives in the rack. Not a good use of my clock cycles since he's a CLI junkie... and those clock cycles and memory represent another couple of users under load.
In anticipation of growth we have moved to in in house solution. Our firewall feeds multiple zones. the server segment includes a file server, a communication server which uses Zimbra for email, eJabberd for in office chat, and Asterisk PBX , an application server which supports our CRM / ERP and KB / wiki services as well as an internal Drupal web server.
The web interface allows single click access to the other servers services (eg. clicking on the client's phone contact will dial the phone number in the PBX and connect it to the user's extension), or in reverse where the client's caller ID will bring the client data to the screen of the user who is taking the call. When a call is transferred to another user, the first user may type a note in the chat window which will appear on the second user's screen. We have found that most issues can be resolved in this way without even transferring the call.
Maybe we were asking a little much from Zentyal, but I believe we should ask as much as possible from or open source vendors so their products become superior to the closed source offerings... and before you ask, we are evaluating the marketability of our solution.
