we're going toward a religion war.. anyway..
Small Business Server has Exchange, SQL Server, and a few other options depending on the version,
exactly, "depending on the version".. SME hasn't such a limitation
and Active Directory. AD creates a 'domain' that users and other servers can join. When they join, they are given rights, and you can control their access to files and services, and allow other servers to trust certain users without a lot of intervention on your part.
this is partially true even for SME
Exchange is basically a central database of email that can be backed up live, and has other benefits, like the calendaring mentioned above.
in my personal experience, "benefits" and "exchange" are words that can't be in the same sentence without a negation.
about exchange's mail storage, it's well known as a nightmare for sysad.
SME, as almost every linux distro, save each mail in a single text file.. this has many advantages: first you can backup them live, then you can compress them easily..
with SME you don't have any limitation about users, mailbox etc.. (depending on your HW)
Windows really shines at basic file and print sharing
strange.. on the same hw and lan, a customer of mine has noted a big improvement in speed form sbs2003 and SME..
, and it runs easily on any hardware you can think of just because there are drivers for everything.
that's partially true.. one of the advantage of linux is that drivers are written for specific chipset.. so, passing from debian to centos to slackware, the same lan adapter will behave in the same manner.. and two different adapter with the same chipset will do the same.. with windows you have drivers written from manufacturers.. two lan adapters based on the same chipset will work in different way according to their drivers..
But I would never attach a Windows server directly to the web, so I dont use Windows servers as gateways or firewalls. I install one nic in them and hide them behind a firewall.
generally speaking, putting datas and users on the firewall is not a good idea.. that's why I prefer SME in server mode with a good firewall
SME really shines at webserving, virus & spam scanning, firewall, email, (with pop3, imap, and horde) and you can serve files, although I'm not conviced that samba is as good as windows with heavily used database files like MS Access. But do you really want to store your files on your firewall in any case?
about files on firewall: see above
about Access: tecnically speaking, it's just c**p, as it's a multiuser db when user's number is less than 2
SBS, and the software to do backups, etc. is very expensive, while SME is priced right. But if you need SBS, cost isnt really an issue...
the right question is "why would you need SBS?".. I mean: if you really need exchange or sqlserver, you'll not buy SBS but you'll use different server for different tasks.. exchange on one server, sql on another one.. if you buy sbs you really need a lot of ram and cpu and, in any case, you'll never be able to get all the power.
and finally, one thing where SME and linux are unbeatable is logging.. EVERYTHING is logged, logs are in plain text.. troubleshooting with linux is undoubtedly easier than with windows
just my 2c
Ciao
Stefano