[schneidmaster]

It looks like they're going to be monetizing by partnering with specific retailers. From the plugin description:

> Buy Happy retail partners will soon be giving you deals to share with friends and family via social media. And we’ll be adding more powerful features to Buy Happy as well — while building a fun community along the way. Isn’t it time to add Buy Happy to your browser?

[mynameisfiber]

Also, don't forget the data they are harvesting. From their privacy policy, they are monitoring your shopping habits and what you do before/after you look at a product. So, that will let them "support our relationships with the operators of the retail websites from which we 
provide you with information about lower priced products"[1]

Basically, this is a data-farm.

[1] http://buyhappyapp.com/privacy-policy/

[ericn]

We would like to partner with retailers directly to get offers they cannot advertise on their website.