There's no mandate in my company that users stick with Google Apps for calendars, groups, document sharing, etc. But any department that went with their own too

There's no mandate in my company that users stick with Google Apps for calendars, groups, document sharing, etc. But any department that went with their own tool for any of that would be their Island that wouldn't interoperate with the rest of the office. That doesn't mean that Google Apps is the best tool, or even that it works well for everyone, but it means that people are willing to put up with a less than perfect solution that's integrated with the rest of the company.