Not only have I used BSD, but I'd say that it shaped my adult life.
As a teen, I signed up for a UNIX timeshare service that utilized a Sun SPARCstation running SunOS 4 (4.3BSD based). You got a Csh and a T1 to the 'Net. When they started offering SLIP service, I installed AmiTCP, an Amiga port of the NetBSD network stack which also included many
I eventually took the plunge and installed NetBSD 0.9 on my Amiga 3000. Later, it was FreeBSD 2.x on my 486/66. While most people in my university programming classes were using Turbo C, I was using GCC. Classmates took MFC/C++ as an elective, I took Perl. Friends were using IPX on their home network, I was using TCP/IP with a FreeBSD box acting as a dial-on-demand gateway.
Having so much networking experience, I drifted from the programming side of computers into networking. My experience with BSD eventually landed me a job with a networking startup that used an embedded *BSD OS as the base for their product. Since then, I've used BSD based gear from Citrix (Netscaler), F5 (BIG-IP, EDGE-FX and 3DNS), Nokia (IPSO Firewall) and Secure Computing (Sidewinder firewall) as part of my job. I've been at it for over 15 years.
I still use FreeBSD for development here at home. DragonFlyBSD is also nice, though I prefer Ports over Pkgsrc, which is why I stuck with FreeBSD.