my nephew built himself a similar system a few weeks back... for a minecraft server
but... I've been thinking about building one myself for the CCTV at work
planning on an upgrade to IP cameras soon, all the extra cores would help with the video processing/encoding/compression etc...
have 16 analog cameras right now, with digital will have at least 20 at 3megapixel each... no idea on data throughput but guessing it'll be quite a bit
EDIT: raw data is 2.5tb per camera per week, or 300gig per hour for all cameras together :-o