RNA - Realtime Network Awareness
from what I know this passivlely monitor network for information about the network(MAC's,IP's, traffic, etc...)
and I heard that this is a seperate box that you use in conjunction with their management boxes

You shoud goto sourcefire's site, they have more info on it.

Other than snort I havent seem much good come out of sourcefire. For having such advanced technology their management console and user interfaces are really bad.

I guess it depends on what kind of money and how safe you want to fell about your security.

There are free tools to do the things sourcefire is doing
ACID, MYSQL and snort can be put together for free
And you could look into something like disco which does passive OS fingerprinting for FREE..

Or if your looking for enterpirse security then with network awareness and with IDS/IPS:
Id say look at Demarcs new Sentarus line, then you could get a better product with all the features you get in 3 sourcefire boxes for a lot less money

Or if you currently have a sourcefire management console ( if you do I feel sorry for you) then maybe you should talk to a rep at sourcefire and see if an RNA box can fit nicely into your current network configuration