Facebook's new Places application promises to be a great way to get deals:
I walk into Domino's Pizza, Places sends me a coupon for $5 off if I spend $20 or whatever.

What will be even better is when I walk into Pizza Pizza and Places sends me a coupon for $5 off if I walk across the street to Dominio's.

So why isn't there an equivalent app on the web? 

Right now I'm doing my Christmas shopping on Amazon (going through one of our local Bitcoin cash-back Amazon affiliates, of course) and I'm wondering why Borders isn't sending my a virtual coupon on my screen when they see me searching on Mark Steyn's Lights Out: Islam, Free Speech And The Twilight Of The West.

Well I'm not really wondering of course, because Borders doesn't know I'm on the Amazon website right now.

So does anyone know of an app or browser extension that would allow the above scenario to happen?