When we first looked at Google Apps in the fourth quarter of 2008 we knew it wasn't ready to run a business. By June of 2009 we were rolling it out to businesses that didn't need some of the functionality Google was still promising at the time. Since then Google has moved remarkably fast to provide additional functionality.
Google rolls out new functions as they develop them, allowing people using their products to be beta testers in their live environments. In my days working for enterprises, this would have driven our IT departments nuts, but it's a new IT world out there.
Of course, software vendors have always done that, but they called it version x.0 of their products and said they were ready for prime time when we were all, in fact, beta testers. Microsoft usually needs a couple of service packs before they get their products right (Vista being an exception - it never worked). Then when they get a product bulletproof, they force their customers to a newer and less stable version (see Windows 2000, Windows XP and Windows Vista/7).
Some users have found Google support for Google Apps problematic and the Outlook sync has had issues. On-Site Technical Solutions has been able to work through all of our issues with Google Apps and find it enterprise-worthy. Whether a business will use Outlook with Exchange or the Google web interface is strictly a business decision, much less a technical decision.
Here, from CIO.com, are four cases where a business migrated to Google Apps and then went back to Microsoft.
The Trouble with Going Google: Four Reasons Why I Got Out