I saw this a few days ago and have been meaning to do a post on it.  Google has finally packaged and released the functionality picked up via the Postini acquisition.  As anticipated, pricing is pretty reasonable but Google still needs to prove it can actually sell something besides ads:

• Google Message Filtering ($3 or €2.00 per user/year) provides basic spam filtering for any email server.
• Google Message Security ($12 or €8.00 per user/year) provides
  comprehensive email security and policy management for inbound and
  outbound messages.
• Google Message Discovery ($25 or €17.50 per
  user/year) provides comprehensive security, policy management,
  archiving, e-discovery for any email server.

Will companies take their approach to message security, filtering, and e-discovery seriously?  To be determined.   Safe to say there would be some hesitancy to having ads served up based on the indexed content of a company’s email archive (not part of the offering…but one must wonder).  Given what I repeatedly learned about the sensitivity and seriousness around corporate email, I’d imagine these needs will continue to be addressed by companies like Orchestria and MessageGate (I previously worked at both).