Having recently installed VMWare Server, I went on a "installfest of one": Windows Server 2008, Kubuntu 9.04, OpenBSD 4.5 and OpenSolaris 2009.06 are now happily chugging along on my server (which is apparently handling the situation without breaking a sweat -- impressive), with Arch Linux next on the list.
I have to say that I've been surprisingly impressed by the two "most commercial" offerings.
Windows 2008 feels really fast and lean. I don't like the new filemanager, but it looks like some of the infamous Windows bloat has been removed here and there. Getting asked for the Administrator password every 5 seconds is irritating, but at least the "Run as Administrator" menu item is more accessible than it used to be, so you can (mostly) preempt it. Also, it seems to work better with Samba, but this might be because Samba itself improved a lot (probably thanks to certain EU antitrust actions, but I digress).
I was even more impressed by OpenSolaris. Booting in a LiveCD before installation is always nice. The customized Gnome 2.24 (aka "Java Desktop System") is the most polished Gnome I've ever seen. The package manager makes it easy to get additional software (and to get rid of unwanted megabytes of localization files for all sorts of languages). It was a breeze to install NetBeans and its plugins (Python support!), I'll have to give it a spin. It's also curious to see in action Sun's typical "network philosophy": for example, /home folders are NFS mountpoints, which makes a lot of sense if you think about it. The drawbacks are that some things don't make sense: e.g. the Gnome utility to track free disk space goes bonkers (34 free gb when the disk is only 10...?). But these are details. I'd really like to spend some time learning permissions, ZFS, zones and all that; I hope I'll get some time at work.
In retrospect, configuring my first DNS server on OpenBSD 4.5 was almost uneventful. I'm not sure I even understand what I did, but it works :) I plan to expose this box to the Big Bad Internet at some point in the future, does anyone need a bit of space?
I guess the moral of the story is: VmWare server is very nice, when you have the right iron to run it on ;)