OpenBSD is much easier to install and get working than any of the Linux distros you mentioned. Post install configuration might take all of an hour, and it's secure by default, unlike those mentioned.
And by "post install configuration," I mean adding XFCE or other DE or WM, along with whatever apps you like. No tweaking needed to close security holes.
There’s a bit of silliness with resource limits (that I think should be configured to match the user’s hardware or at least mentioned in the installer), but overall I agree completely. The base system includes a couple of window managers, including CWM which is quite nice. On a laptop you have to enable APM, but after that you’re just about done.
I’d say it’s about equivalent to a simple Arch install on easy hardware, although OpenBSD comes with quite a bit more security stuff pre-configured.
I haven't touched any of those Linuxes yet run FreeBSD as my primary laptop OS, a home server and a few remote servers just fine. It takes more time to get FreeBSD running properly than, say, Debian, but nothing to put new users off. There are HOWTOs on how to get it quickly operational on a solid level, for example, for desktop use [1].
While you're doing the initial configuration, you get to learn a good deal about what the OS is made of. I found investing a little time to get familiarized with the system components results in more confidence as a user, rather than simply letting the OS do its magic and then wondering how it works later on. Like moving into a new house... You want to know where the fuses are and how to shut off the gas valve.
I suppose I could agree if only so the new FreeBSD user has a reference to compare by going through what the guys on the other side of the tracks have to do to rebuild everything from source, kernel and ports. For FreeBSD users its a pair of svn updates, a make world, maybe a reboot, and a portmaster -fa. From what I remember with slackware and from lightly reading advocacy threads like this one it's unusual for linux folks to build their own anything with the exception of the kernel.
I’d go so far as to say that you shouldn’t touch a FreeBSD or OpenBSD install unless you’ve already done and maintained a gentoo, arch, or LFS install.