I have used PC-BSD. I use FreeBSD and used to, and will return back to, Gentoo/FreeBSD.
Only thing common between linux and a BSD is that they all are Unix like/compliant systems.
Linux is more poised towards System V and BSD's towards BSD4.4, AFAIK.
There's a lot of difference at the core like different kernel, file system, support for hardware, binary types, c library, make system and more.
Two issues that I faced are, flash support is really bad due to adobe not having native flash for BSD's so you have to rely on linux compat for that. Secondly, support for virtualisation is really pathetic.
Things to look out for - FreeBSD jails, zfs support, pf firewall got from OpenBSD.