I'm still not seeing how tracking a stable release of FreeBSD is any different from tracking a stable release of Debian, or the same for unstable releases. If you need a controlled environment for producting, Debian stable or FreeBSD 4.x are equivalent. If you need an up to date environment for hacking or for personal use, then Debian unstable or FreeBSD 5.x are equivalent. Is there something I'm missing in that picture?