Here I am going to put my thoughts for these differences.
1. Facebook have the notification bar which enables user that they got some updates. But in Orkut we have to remember the number of scraps you have after that you can calculate that you get an scrap.
2. Facebook have the like button which is the major part of it. We can like any thing from the friends status to brand.
Facebook have universal like button.
3. Facebook have ability to fetch the web content however Google Orkut does not support it.
4. We can merge the Facebook share button to our site or on our blogs to share the content of our products. While Orkut does not have feature like this.
5. Facebook is easy to access while in compression to Facebook Orkut is little bit diffcult.
6. Brand promotion via Facebook is easy.
7. Facebook have the timeline feature while Orkut supports only the themes.
8. Facebook runs on the PHP platform while Orkut is on Dot Net platform. PHP platform is faster than the .NET.