iCloud, iCal and Mail integrates pretty well with Google Calendar, even though they are not both from Apple.
But I have a hassle when it comes to Calendar Notification in Mail App specifically.
I get notifications correctly on OS X, iPhone, about Google Calendar. But, my Mail.app keeps trying to send me emails about my notifications, so I either get duplicated emails (from both Google ou Apple) or, nowadays, I get hundreds of Draft in Mail since I've got 2 SMTP address from both accounts in Mail and it prompts me in each to decide which server show be default.
The thing is. I don't want either. What I really wanted is that Mail could stop sending me mail alerts, but keeping Google Calendar and iCal/iOS calendar in sync.