I was thinking about this last night, we have 2 separate apps (which means 2 separate windows) for something that so intertwined as your email and calendar. Not dictating what it should be like, but would like to hear what you guys think about that? For me personally, having fewer apps where it makes sense is desirable. For lack of a better example, this is how Outlook works and it's been pretty solid so far. Of course, the easiest thing to do would be to go use Outlook then, but I much prefer Mail and Calendar.