I've been calling Facebook Notifications the Push Notification of the Web, they are great, maybe just as good as native Push Notifications. But they have also "solved" (it's new and yet to see) the spam problem recently by implementing harsh restrictions on how you as a developer can send them. It would be interesting if Apple and Google copied this behavior. Basically Apps that send > 50000 notifications a week have to maintain a 17% Click-To-Impression ratio. However I find the 50K an oddly picked number which should instead be based on installed user base.