We used FreeBSD exclusively at my first startup in 1999 (flashbase), partially because of Yahoo's success with it (I was at Stanford). We found the base OS to be very stable and the networking stack to be especially robust. But, the mysql port was not that stable and drivers for proprietary products, like Oracle, were hard to come by.
Back in the day, Oracle did a freebsd driver partially for Yahoo. The Oracle drivers were not open source and hence there were few options to connect without Oracle's help.
I worked in the kernel networking group at SGI in the 90s and there was a lot of freebsd loving there. Also, the FreeBSD license was more relaxed and commercial products (like NetAPP) could include and extend FreeBSD without disclosing their modifications.
Our frustration with lack of support for FreeBSD moved us to choose Linux and Windows (for SQL server support) the next time around in 2004.
