This is a 20% project. While it's one we plan to use internally, it's not a "supported" Google product. It's just another open-source project along with the many others we use to keep our networks secure.
Also, it's designed specifically to do one thing (packet history) and do it well. In no way is it a complete solution; this is a building block for network detection and response.
To reiterate some of the salient points:
1) Disk is REALLY cheap these days.
2) NIDS don't store lots of history, because they're optimized for detecting patterns and signatures. So they might find something in the middle of a TCP stream and send an alert, but you don't have much context around it. This allows you to build that context by requesting all packets from that stream during a (possibly very long) time range.
3) There's a ton of reasons why this isn't used to monitor users:
* it's wrong: I'd flat-out refuse to build something designed to monitor users
* it wouldn't work #1: most interesting user traffic is encrypted on the wire
* it wouldn't work #2: our production network architecture is not good at single aggregation points
* it wouldn't work #3: there aren't enough disks in the world to handle our production network load
* it's redundant: applications can already do per-application, structured monitoring as necessary for debugging/auditing/etc.