Google improves it's user experience day by day. The new feature is pretty cool ! For example, if you were googling about a new car purchase, Google Now will alert you if you are near a dealer that sells that car. If you just window shopping online, this might be an issue. But if you are just looking after something specific, this might be pretty helpful.
We don't know yet if Google Now will have some customizable options or not. For example, if you just look online for items, Google Now will pop up dozens times a day when you are in the city, and this can become pretty ugly. There it could be an option to stop those Google Now cards or just to set to pop up cards below a sum limit for example.
Another question for Google is: when Google will know that you bought the item that you want and it won't pop up anymore cards for you? Or, if you work near a mall, those cards will pop up all the time?
For me, if I search something online, 90% of times I will buy it online, so I won't need Google Now suggestions. But this feature seems pretty good for some customers, but it needs some adjustments to work perfectly for everyone !