During his presentation, Jyri talked about his five key principles for building sites around social objects. They are:

1. Define Your Object: This is the easy part, but perhaps most important. The social object will be the center of your network. On eBay, it's whatever item you're selling or buying. On Amazon, it's a product. On Flickr, it's a photo and so on. 
2. Define Your Verbs: This means what do you want people to do with your social object. Do you want them to comment? Rate it? Share it? Watch it? Etc. Make sure whatever action they should take is clear and highly visible on the site.
3. Make the Objects Shareable: This is almost a no-brainer, but you would be surprised how many sites have not made it easy (or even possible!) to share the object which their site is centered around.
4. Turn Invitations into Gifts: Want your friends to join you on the network? Don't just spam them with an invite, send them something of value. Jyri mentioned how a purchase of a Skype headset years ago also included a set for a friend. Also, PayPal had originally offered a small amount of money posted to the account of your friends who signed up for the service.
5. Charge the Publishers, Not the Spectators: On any network, there are those who are creating and those who are passively consuming the content. You shouldn't charge the latter, only the former. The people who are actively using the service and are getting value from it in some way are the ones who would be willing to pay for additional features or, in some cases, just to use the service itself.

An interesting parallel to #5 is the online news industry. Today, many publishers are tossing around ideas about charging for their online content. This actually goes against his final key principal, which may be why some of those ventures won't be as successful as the publishers hope.

Although Jyri Engestrom has not published the slideshow that he used during the presentation, the one embedded below has many of the exact same slides, including the five principles. However, you may be surprised to learn that this one was uploaded to Slideshare two years ago. Even though, it seems the subject matter is still as relevant today as it was back then.

Do you agree that these principles have held up over time? Or does this list need to be modified or changed in some way?