For most server setups OpenBSD's hardware support is adequate, and this is especially true for VMs. It's laptops, peripherals, and bleeding edge, high-performance or specialized devices where driver support is a PITA. But that's not something I've encountered running my own private servers. It would be nice to have something like ZFS, but mostly that's a peace of mind and convenience thing--would be nice to be able to stream backups somewhere rather than push around dumps and tarballs, though I have a script for that.