Hello there !
THis may or may not be helpful for you, but since my setups are pretty much common these days I will give my opinion on SME Server.
1. I use it since 4.2. Have no idea when that was, perhaps in 2000-2001.
2. I use it at home, at office, in neighbourhood nets, on crap hardware and virtual machines, as well as dedicated machines.
3. I use these features:
-proxy+the filtering it provides
-http
-ftp
-pop
-smtp
-imap
-VPN
-clamav
-spamassassin
-router (plus some hacking I did for a couple of them)
-mysql
-Samba (heavy usage, including truecrypt volumes hosted on SME and mounted on workstations, backups, some kind of NAS also with many TB of data)
-games hosting (emulators in java for LAN parties and such, even counterstrike servers a few years back)
-ISP (hosting space for friends with some contribs like userpanel and awstats and the like)
What I did not use so far is SME as PDC, but I am planing for the future when windows 98 and XP Home stations will get upgraded AND there will be a stringent need for it.
SME also seems not well suited to do advanced QoS for a couple of reasons, even tho some contribs exist, but where i needed it i preffered things like IPCop, Brazil and other dedicated firewalls out there, at first because I was more used to those and they are made for that purpose, now because it does not cost much to virtualize those too and get a headache off my head.
Again, virtualization offered me the resources to split SME services into more machines. Like one for mail, webmail, FTP, webdav, and related stuff which is exposed to the internet, another one for Samba official (files for work), one unofficial (ppl share personal stuff, pictures, movies from parties, meetings, hunting, backups from their laptops and similar stuff so I dont have to backup those twice a day like in the other server and not provide them any excuse to clutter it). Also made it very easy to backup those servers.
I have some more as "MX 20+" machines, because power is not so reliable and we have lots of offices which needed gateways anyway so no mail is lost ever.
I am not a SME fanatic, I do use many other distros, but SME does my job quite well and of total number of servers i am looking after, they are the main bulk and the ones requesting the less attention.
If you need a scalable solution, SME comes the closest to one size fits all I ever met. Many customisations are available for ppl that know what they are doing, heck, it can be a fax machine, a PBX, i wonder how long till it will cook the food for me and buy groceries...
I feel very much in debt to the ppl that make SME Server OS for saving me a lot of time of my life and allowing me to manage 20+ networks, each with different characteristics and needs.
So far, at a small scale, SME can do everything, it can be customized, can use updated packages when absolutely needed and uptime and/or security are not stringent needs, for example in home and residential networks, but in production environments, I would never suggest tampering with it unless you are a linux guru+SME templating and anatomy expert in which case you are either a developper or you do not need SME at all.
For me SME saves time in many places:
-upgrades
-installs
-security auditing (never got hacked, at least I dont know of any such successful attacks, even if at times some ppl "forgot" to update phpBB, image galleries, webftp and other security nightmares out there)
-back-ups
-and last, but most important, reliability.
Thank you SME people, this is a project which has way too little fame for what it is worth. Windows servers do half the job and cost loads of money, while SME is something different tho does the same job and more, needs a different way of thinking but offers more options in a more secure environment, an unlimited number of installs and users, it is the difference between work and fun.
I have fun at work and I work having fun for friends and ppl I know and SME Server is part of this fun.
But most of all I enjoy the freedom. Number of installs, concurrent connections, those were never a problem for me while others struggle with this every day. Virtualization allows me to run many servers while lessening the electricity bill and pollution, simplifies the back-ups, reduces downtime, increases redundancy, add to this SME server and we have the wonder admin that manages almost alone 15+ servers at work and has time to SSH into others, in order to troubleshoot or add some hacks.
M