I have worked with Berkeley Software Distribution (BSD) UNIX in a number of incarnations including:

Additionally, I have worked on many commercial UNIXs that were heavily influenced by BSD including Dynix/PTX (Sequent) as well as UNIX variants from the Open Software Foundation (such as early HP-UX).

Because my focus has always been commercial applications of UNIX to business issues, I have not spent as much time as I should keeping up my BSD skills.

For example, I will grant that the BSD releases of UNIX for Intel offer some of the most reliable, robust and secure operating systems available at any price. My concern is that lack of vendor support in the way of device drivers and commercial sofware support along with BSD's long roll out cycles (for extensive security auditing) limit these systems to roles as appliances (mail server, web server, firewall).

For these reasons, I prefer to concentrate on Linux where commercial support is there (everybody but Microsoft) for both hardware and software.