By bending over backwards to accommodate Outlook holdouts, Google is weakening its case for the use of Gmail and Apps, Pray said.

Google holds a different view. The goal for the first version of Apps Sync for Microsoft Outlook was to meet "90 percent to 95 percent" of Outlook users' needs, which was accomplished, said Rajen Sheth, Google Apps senior product manager.

That includes the synchronization of e-mail, calendar items and contacts between Outlook and Gmail in "much the same way" as it works between Outlook and Exchange, he said.

While acknowledging that the tool doesn't offer full feature parity right now, Sheth promised that Google will extend its functionality aggressively.

"As you know, with Google, our first release is never our last release. We have a strong philosophy of getting something out there in the market that is strong and meets the needs, but then continue to iterate on it to add more and more functionality," Sheth said.

"You're going to see us do that aggressively with this product, just like we do with everything else. We'll continue to add releases to it, to add features, to make it better and better and go from 90 [percent] to 95 percent to close to 100 percent of the use cases," Sheth added.

Many people embrace Gmail's end-user interface when their companies adopt Apps, but companies of all sizes have vocal contingents of workers with a deep attachment to Outlook, for which the IMAP synchronization falls short, he said.

"There's a specialized experience that Outlook users have when using it with Exchange Server, and we wanted to make their experience with Google Apps to be as close as possible to that experience," Sheth said.

Google remains convinced that what it views as the benefits of the Web-based Gmail user interface will continue to be recognized in workplaces and will win converts even among Outlook die-hards.

Outlook loyalists can be found even in places that help companies adopt Google Apps, such as systems integrator Epicentro in Milan, Italy.

Epicentro provides Apps implementation services and has also used the suite internally since 2006, when it migrated from Exchange to Gmail. After several years, it still has "a few active users" of Outlook, said Mauro Ginelli, a Google Enterprise Applications specialist at Epicentro. After testing the plug-in, Epicentro plans to install it on its Outlook users' computers.

Ginelli thinks Apps Sync for Outlook will help convince potential customers to switch from Exchange to Apps. It gives Outlook users synchronization for e-mail, calendar and contacts, and can smooth out a progressive migration to the Gmail interface, as opposed to sudden and forced transition, he said via e-mail.