A few] years ago I was just getting into system administration. I learned Linux first. Then one of our old (I mean *really* old) BSDi servers crashed, and it was up to me to rebuild the system.
I looked at FreeBSD, NetBSD, OpenBSD and Linux. In the end, it came down to "secure and stable" that took the prize. OpenBSD 2.1 was installed.
Since then, I've run 2.1-2.5 on everything from production servers to laptops. We've never (repeat: NEVER) had a break-in.
A coworker setup a RedHat based box to test his skills at setting up SSL and a secure web site. It was hacked literally overnight, and by the next morning was attacking other sites.
Our OpenBSD servers were probed and then left alone.
In the intervening two years, that original server got upgraded and patched several times and the OS never gave us reason to question the reliability or security of OpenBSD.
We have another box, acting as a router for about 800 workstations doing very basic filtering and NAT. It's on a P120 with 32MB RAM and typically the uptime would look like this:
% uptime
9:05PM up 266 days, 4:23, 1 user, load averages: 0.06, 0.06, 0.06
%
As well, OpenBSD runs on my laptop. A Gateway Solo 2500 with a Xircom modem, and a Linksys fast Ethernet NIC.
And it never crashes :)
One other incident that made me a believer... we were pingbombed [perhaps a predecessor to the early2000 DDOS attacks?]. I mean, 900 different hosts on different networks floodpinging an OpenBSD 2.3 box simultaneously, while it was processing email and web pages for 3500 users.
It was a P133 with 64MB ram. And it didn't go down. It got a bit slower, but never crashed :-)