BSD, the Berkley Software Distribution, is one of the least-used variety of Operating System in the world. BSD has been around for a very long time, even before the times of Linux. It is a version of Unix, the grandfather of most Operating Systems. Technically, Mac OS X is a fork of BSD, which is what allows OS X to be POSIX compliant.
There are a few choices to choose from with your distribution of BSD. Like with GNU/Linux, hundreds of them exist. The more popular ones are FreeBSD, OpenBSD, and PC-BSD. PC-BSD is the only one of the bunch that comes with a graphical desktop environment installed by default, so it is considered the "newbie" BSD. Debian is creating a variant of their OS with the BSD kernel and intends to turn it into a major project, but it is still in early development.
FreeBSD is know for its speed. Speed and performance are the two major selling points for BSD; it even claims to run more efficiently than Linux. FreeBSD is not for the feint of heart, however, because it will take some expertise to get it running properly and to install graphics if that is what you wish to do. You will also have to deal with some outdated repositories, since porting them to BSD takes time.
OpenBSD is focused on providing an extremely secure operating system. I can't vouch for its security personally because I never used it on a server, but it seems to be the choice for companies or individuals who want a secure desktop or server.
PC-BSD is the most user friendly version of BSD. It is criticized for coming with a lot of "bloat" preinstalled. Other lightweight versions of BSD do not come with a lot of features installed, usually just a compiler, a text editor, and a few other tools that can be used from the command line. PC-BSD on the other hand comes with X, a graphical desktop environment, and a few graphical tools that other versions do not have preinstalled. If you are new to BSD, I would greatly recommend PC-BSD as a starting point.
Above are my opinions on some of the various distributions of BSD, but I feel differently towards BSD as a whole. I feel that BSD is far behind Linux in terms of support, package updating, and user-friendliness. The first kernel panic I ever experienced was actually in the LiveCD of PC-BSD. Also, the BSD license allows others to edit the source and turn it into proprietary software, which I don't support morally.
In conclusion, *BSD is great for heavy server use, but for practical desktop usage you should go with another alternative, like GNU/Linux.