Yeah, I think it is the most secure, nobody's gonna make a virus for a BSD system, but then again, how many people would program applications for it? Oh, and before you post "DOS is more secure", I'm talking about GUI, which means Graphical User Interface. I also think BSD is more secure than Linux.
tapwatah: If I knew how to make a virus for BSD derivitive OpenBSD, FreeBSD etc I would do. Given that an awful lot of websites are running Apache on top of *BSD or Linux makes sense to exploit this. As it stands OpenBSD is generally the most secure if you go by the number of exploits within its userland and tool chain etc.
Loonylion: True the whole permissions system makes it damn hard to cause havoc. But its still possible. There have been kind of viruses, but the were very specific in what they targeted. The bigger threat at the moment seems to be rootkits. Just looking at Rkhunter shows a long list of detected rootkits. But as you said, a poorly configured BSD system is wide open for attacks, just mis-configuring Apache or OpenSSH can cause a whole heap of problems.
dont also overlook that people who use linux/unix/BSD are often a lot more wide awake to what is going on in their system than windows users.