I think that everything that fosters communication is addictive. If you think about it like this:
- Email, the original means of Web communication, was very addictive. Do you remember the days back in 1995 when you typed and quoted people's emails for 4-page long and conversations which lasted over months?
- Then IMs came about, and that was essentially a digested form of email, except that you don't really have to edit much because it's not very formal.
- People like to voice their opinions and made themselves heard, not just to a single person, but to many at once--that's where chatrooms come in, allowing individuals to broadcast their opinions to a group.
- But chatrooms are instantaneous, and are not permanently stored, so most don't find that extremely effective. That's when you have blogs, where their opinions and discourses are permanently stored on databases, and remained indexable and thus searchable by search engines.
- Blogs require authorship, and most don't have the time to do that, and that's where comments came in. Friendster was originally very viral, but Friendster calls them testimonial, and testimonial sounds very serious and so it never really kicks off.
- Comments, like IMs, are intentionally casual, so people write more often. What makes Flickr popular is that users can submit whatever they want to on the Web (a subjective perspective), and people can write whatever they want. Its database is hosted by Yahoo, and so it becomes very searchable. In fact, you will find your Flickr comments get onto Google index within 4-5 days (I subscribe to my own Google Alerts so I know that)
- Facebook is addictive, possibly because it allows you to install multiple applications based on interest, which is the link that link people together originally anyhow, and connect them together (see SML Pro Blog: Innovation = Synergy of Existing Ideas). In other words, Facebook creates multiple points of entry for communication. If Flickr would allow users to easily comment on other people's tags, date, EXIF info, etc, it might make it an even more interesting product. The notes feature is definitely a pro.
Mashing up your life
An easy way to mash everything up would be even more powerful. I am working on a project to mash every single social network that I have a presence in. This project, code name SML Lifelog, is a venue to provide multiple points of linking possibility to create a summation of all the social networks where I have a presence (See SML Network), and foster the ability to comment on a single topic spanning multiple networks.
Hopefully, when the product get onto beta in 2011, it will be more addictive than any networks you find today :)