Postini provides archive, security and compliance services and dovetails nicely with Google apps. Google apps has seen a following develop since it combined Writely functionality with some of the core Google stuff. Iit is now at the point where it’s value has been proven.
What Google hasn’t yet proven is the corporate level archival and complaince requirements. This lacking has hampered the ability of Google apps to roll out to the “higher level” users. It’s still pretty much an IT geek and interested eccentrics solution. Large scale corporates, Government departments and the military require a high level of compliance in terms of security and archiving. The Postini solutions, linked to Google app, will give them this.