Google Apps is great, until Google decides to remove a key feature and replace it with an updated feature at some undisclosed time in the futura, ala Google Docs offline suite that used to work great with Gears.
It's also been my experience that Google doesn't really seem to understand what "enterprise" support is. "oh, gmail is down in that part of the US, it will be back soon, thanks for using Google."
Finally, you also need to hope Google doesn't piss off any other countries, like they did with China, forcing my company to add more VPN capability to access GMail from China. I have an email from a Google VP assuring me that Google would work hard to make sure that it's services would remain available in China without a VPN. Recent calls to Google support about connectivity issues...are basically "sorry, it's not our fault, use a VPN, we can't/won't help you. Thanks for using Google, this support incident will be closed"