I don’t think it is like Stumbleupon, social bookmarking or facebook apps. With those sites/technologies, the early adopters saw huge returns. It wouldn’t be the first time I got it wrong though. No rush here, but I have my eye on it.
IMO, If there is a compelling reason for the average user to switch from facebook to google, they are not getting the message across and it’s like online auctions or classifieds their SHOULD be only one.