For example, changing the IP address of a machine running OS X Server screws up things like Open Directory.
Maybe so, but that's only if you enable Open Directory and configure the machine to use it for authentication. At least in Panther Server, a "standard" user would probably stick to the default NetInfo database. They'd have to go around and change things to get Open Directory. Maybe that's different in Tiger Server -- I don't have direct experience with it.
There's quite a detailed, command line, set of instructions that have to be followed in order to keep all of the services on the machine functional. There are also security implications if the user does not correctly configure and maintain the system, given the extra services that are running/can be run.
Huh, what? Again, is Tiger Server such a horrible product that it requires this constant maintenance or it'll go down in an instant? I find this extremely hard to believe. For me, Panther Server was a breeze to setup and it remains running quite well to this day without any maintenance. Just like the client version. What is all this extra maintenance that you speak of?
As for security, I don't know off the top of my head what extra services are enabled in the default OS X Server install, but they're all incredibly easy to turn off or firewall off in Server Admin. Really, that's the whole point of OS X Server -- the heart of it is in the nice admin tools you get.
Installation and maintenance of servers should indeed be done by experienced persons, but having OS X Server available for free means that any old sod is quite possibly going to select it regardless of whether they need it or not.
I think we could end up with a glut of users who are trapped without software support and wonder why the hell they spec'd a server operating system for their desktop.
I'll say it again - I love OS X Server, it's fab, but it needs a premium pricetag to keep it from ending up on consumer machines.
You're right in that the server admin tools expose extra settings and functionality that are hidden in standard OS X. But is that really such a huge problem? I don't see it. It's easy to screw up the standard OS by changing certain settings or deleting certain files. At some point, the OS has to assume that the user knows what they're doing and let them. Otherwise you get Vista's "security" features.
Inexperienced users come in two flavors - those who don't touch anything they're not comfortable with, for fear of messing something up; and those who blindly click and change settings and hope for the best. The second kind will do just as much damage in Server as in standard OS X, and I'd argue the first kind won't do damage in either case. The click-and-damage users are just getting what's coming to them anyway.
And for every one of those who chooses the "free" Server option that they don't need, I'll bet there's a bunch more power users who either know what they're doing or know enough to research before doing things, and why deny those power users a chance to utilize some of the extra server functionality? It's a big win for them.
As for iLife (commented in a few other posts), of course OS X Server doesn't come with it. No current version of OS X comes with it.
Older versions of iLife refused to install on Server, but for no real reason. The installer simply looked for a certain file that identified the OS as Server, and if you temporarily moved that file out of the way, it'd install and run perfectly. Again, I haven't had any problems with any client-oriented software on Panther Server. I assume (but don't know) that Tiger Server is the same.
my message is don't get OS X Server just because it's free!
My message is
don't get OS X Server unless you plan to utilize its extra features. 
