Years ago my brother and I worked with a friend of ours to create a web startup based on doing Movie, Music, and Book recommendations. 
 
The fundamental technology behind the idea was the brain child of our friend and business partner, Owen. 
 
He wrote a guest blog on Facebook's new 'Like' feature that I think is very good.

There are some fundamentals the even companies like Facebook can misjudge occasionally. Give it read! Facebook like feature.