That's a good post J. I'll add in my opinion on this. I'm a Windows Server engineer by day with my job being mainly installation based of new kit for customers (Work for a large company so there's a constant stream of installation work).
I ran ClearOS at home on a server for a good few years with nothing else. For my needs at the time it worked perfecty and I had no real issues with it (Other than the odd ones I caused myself as I heavily customised it). Back in the day when it was ClearConnect I paid for the Enterprise version to get MultiWAN which came with support. I have to say the support was excellent, I think I used it on 2 occasions and both times was most impressed with the speed and also the fact they were spot on. Now there's not as much information as Windows out there but regardless the support the Clear Foundation provides is top notch.
Then I hit the issue of wanting to run an OpenVPN tunnel on my ClearOS box to route set traffic down it. I know technically this is possible to be done manually but having MultiWAN made the rules just so complex that I gave up. So I switched my system to ESXi and put pfSense in a VM. This runs perfectly for my routing needs and is an extremely good product, but it's only a firewall.
As I was running ESXi and have an MSDN account I thought I'd give a MS Windows Server network a go at home. By this point I'd actually got 2 servers, 1 with 8GB of RAM and another with 16GB.
However the issue is Microsoft wants everything split out normally into seperate boxes in a lot of cases if you want to stay supported. So I had 2 DC's, 1 Exchange 2010, 1 Sharepoint, 1 Terminal Server, 2 File servers with DFS between the 2 boxes, etc. It all worked but it took too much effort to maintain. That and I just don't have enough RAM to do it right. Exchange had to make do with 4GB of RAM for that VM which is below the minimum of 8GB when all roles are on the same box. Even when I gave it 8 the performance is hugely poor vs say Zarafa on ClearOS (Thanks Tim) . Patching it was a nightmare and always requires a reboot in Microsoft's world. The wife is the most unforgiving customer I've come across and the downtime wasn't acceptable to her
I tried SBS 2011 but as I'd added a lot of extra software on it the RAM requirements went through the roof and it was just too slow on my hardware.
I tried Zentyal (As a VM as still keeping pfSense) but it's just not as good as ClearOS. In some ways it is better but it's far too slow on the interface and not nearly as easy to customise config files without it overwriting them.
ClearOS 5.2 took me an age to customise to run the extra software I need because the packages are so old now they need to be updated manually. So I didn't want to spend ages building this up when 6 is also out soon.
So my current solution I'm trying is as follows...
1 x pfSense VM (Routing)
1 x Openfiler (RAID 5 with my storage) sharing out SMB on a seperate virtual switch
1 x Media Streaming VM (Ubuntu with Serviio and AirVideo, mounts Samba share on boot)
1 x Download VM (SABnzbd, Sickbeard, Transmission, Couchpotato, as it's a seperate IP it's easy to route traffic from this down the VPN which pfSense is running. Also it connects to Openfiler with a Samba share on boot)
1 x SBS 2011 still running as I've yet to have the time to migrate everything I need off it.
This is about as far as I am currently. My plan is to have ClearOS 5.2 installed this week with 2 NIC's. One on the virtual switch to mount Samba shares and the other to my LAN so I can add users and groups in ClearOS and people connect to my shares via this, Openfiler won't be visable. I should then be able to lose the SBS 2011.
My overall theory is by splitting them out it'll be easier to upgrade one without affecting the other. So when ClearOS 6 comes out I can upgrade quickly because all my custom software will be running in seperate VM's. Even my flexshares won't be hosted on the 5.2 VM so I'll have little data to backup and move. I can also reboot this, mess around, etc without knocking my Internet off, or downloads / media streaming so the wife will be almost happy (As good as you can achieve I think)
It's a lot of effort but my ultimate point is even when you have Microsoft licenses, it's not always the best solution. It's RAM hungry to the max and needs far more time to maintain in my opinion than ClearOS (Or Zentyal I imagine). However if you want the best of all worlds you'll have to virtualise and run various different products.
I'd give up my setup in a flash though to run just ClearOS if I could have a OpenVPN tunnel and route traffic down it as I choose (Including traffic generated on the ClearOS box). I miss those hassle free years.