FreeBSD Netmap user here. You actually have to recompile the kernel with "device netmap" added in your kernconf. Piece of cake, after 20' you are good to go. But you need a real network card and the FreeBSD driver must be ready for netmap. Using intel 10Gbps adapters (~200euros) is a safe avenue (FreeBSD ixgbe driver). Even in VMWare, you can pass-through the PCI address of the adapter port to your virtual machine and have it talk to the card directly. Everything works very good.

The gain in performance is mind boggling! Trying to sniff approx. 2+Gbps traffic with Suricata using the "normal" avenue of libpcap ends up dropping a small percentage of the packets. And the machine will waste incredible CPU. Using Suricata with netmap (no need to recompile, Suricata pkgng binary build from FreeBSD comes ready) uses exactly one capture thread and drops ZERO packets. This behavior is stable for days!

Netmap is hands down awesome.