I'm running a production server (RAID setup, i7, so decent specs too) with multiple jails, each with their own ZFS filesystem. Honestly, I may be biased since I've been a FreeBSD fan since about '99, but it is really a sysadmin's dream. The system has been rock-stable for years. I'm currently running FreeBSD 8.1-RELEASE. Upgrading from 7 to 8 was not a problem, even from remote.<p>I'm a fulltime developer, so the less time I spend sysadmining on this system, the better it is for me. Upgrading packages, the kernel and even the jails is a quick job and can be set up to happen automatically.