Of course, Google isn't alone in the SaaS market for collaboration and communication software, where Zoho and Yahoo's Zimbra also compete. Meanwhile, IBM and Microsoft are busy re-tooling their on-premise software to work on the cloud as well.

Google, like other SaaS vendors, also faces skepticism over the security, privacy and reliability of Web-hosted applications, which reside, along with their data, at external data centers beyond the control of an enterprise's IT managers.

Still, Google maintains that it is making steady progress at winning over large corporations. Some recent large deployments of Google Apps Premier, which costs US$50 per user per year, include 20,000 users at Motorola, 35,000 users at Rentokil Initial and 7,000 users at Konica Minolta.

On Sunday, Google will announce its latest Apps enterprise win -- MeadWestVaco, a global packaging company based in Virginia that has signed up for 17,000 users.

Currently, Google Apps is in use at more than 2 million businesses by more than 20 million end users, although the company doesn't break out how many of those deployments are of Premier, the paid version of the suite.