I love OpenBSD and have 5.0 installed on a router. But man they are old-school. Just looking at the upgrade instructions[1] brings me back to the time before package managers and makes my long for a nice "apt-get update && apt-get dist-upgrade".
I've never had an openbsd upgrade break, even when I do it the ninja way (which I often do, being a reckless fool).
Despite the longer setup time, I've found that openbsd servers end up needing far less maintenance than any others. It works well as a "fire-and-forget" operating system, a quality that seems to be lacking among the larger players.
(EDIT: not disagreeing that apt-get, yum, and pacman/yaourt are nice. Just talking about how awesome OpenBSD is.)