What are some ways to introduce gamification in a social internet product?

How reward based system work in social sites like Stack Overflow? What are some ways to introduce it in my own product?

What is the difference between Product Designer, UX Designer and Interaction Designer?

I am a bit confused here. Can someone please explain the difference here? Also, how do Product Designers collaborate with Developers to bring the design to the web? Is it always photoshop or do they actually code to create prototypes?