Video suspend/resume requires vt(4) and dri2 to be loaded
Brightness keys work after r270516 (you have to start X at least once); acpi_video works to control brightness with the same caveat
acpi_ibm(4) reports fan speed, but most of the control sysctls do not work
Mute and volume controls work
External displays can be hotplugged while in X, but must be explicitly enabled via xrandr
Booting / disk layout issues
The BIOS does not handle GPT-labelled disks that boot via BIOS (default install layout for FreeBSD). It seems to assume that the present of a GPT means it should expect an UEFI partition. Using MBR partition and BSD label with UFS works fine.
Using ZFS with MBR is reported to not work with FreeBSD's bootloader (but does work with grub) See PR#194359 for the bug report and fix