Whether 3rd party cards in Google Now are a good idea or not depends on as what you define Google Now. When it is made to get to learn you intelligently and to combine all of Google's services and capacities, then third party notifications would probably not make much sense.
But if Google Now is made to show you ‘by the way’ information, which could interest you, but don’t have to. Or that could point you to something which you otherwise also wouldn't miss, then third party cards would make sense.
I made this to see how the flat ios7 -design would look like applied to Mac OS. And I think the result is not too bad. Something like this is also not too unlikely to happen! Especially the dock looked much the same on Mac OS and on #iOS up to now and I think #Apple probably wants to continue this.
What are your thoughts about this? Do you think the iOS7 design would do well in Mac OS?
