Why aren't you using FreeBSD?
Here I sit, watching a freshly installed FreeBSD box run through cvsup on all ports, to be closely followed by a new kernel compilation. As the output flies by in the xterm, I find myself wondering why I don't run into more FreeBSD in the world.
The truth is that I've been using some form of BSD since 1993 or so (the days of BSD/386). A foundational server that I've run since 1995 used BSDi initially, transitioning to FreeBSD back in the 3.0 release days. I can't contemplate using any other OS for this box and the myriad tasks it performs. We're not talking about a system that sits idle most of the time; this box generally deals with 250,000 to 300,000 emails a day (mostly spam, which produces a heavier load than actual mail delivery), and it serves up DNS, Web, and SMTP/POP/IMAP services for dozens of domains. It generally hovers at a load of 0.50 with the occasional spike.