Postini, a company acquired by Google, is now offering enterprise web security. All traffic is routed through Google, and they take care of making sure traffic meets your corporate policies. The interesting part of all this though is how it secures computers, even when they aren't in the office.
According to the Google Enterprise blog, this new system forces users using corporate computers to use the Postini web filtering tool -- without requiring a VPN connection.
Protecting off-network users used to require them to connect via a VPN when they were out of the office — often with mixed results. With this new feature, all off-network users' web traffic is automatically directed to scanning infrastructure to enforce your policies and protect their computers, requiring no action on the part of individuals. It's easy to deploy and users can't tamper with it, ensuring your security and appropriate use policies are always in place. -- Google Enterprise Blog
Since users cannot tamper with it, this service becomes very desirable for network administrators who are constantly fighting against malware and spyware that creeps onto systems while connected to networks outside the company. There is no reference to the cost of the service on the website, but if the price is right, this could be big.