No 2 - Put on real world events
One thing that can really help to build community and social value around a digital media service is real world events. Apparently myspace really took off after they began sponsoring local gigs and even today, marketing efforts are being driven by the myspace Secret Shows events. Building offline community makes your site cool.
Another site that is using events very effectively is Yelp, a local reviews site. Yelp holds regular "Yelp Elite" piss-ups for the Power Users that Yelp want to keep on the site because they post a lot or write good reviews or whatever.
In the words of the CEO of Yelp, Jeremy Stoppelman:
"...we actually hold local events for our hardcore users, we call them the Yelp Elite Squad. When someone gets really involved with the site we try to identify that, and bring them into the Yelp Elite Squad. Then once a month we do events where everyone can get together. It's a way of getting to know those folks and thank them too. There are about 200 of them so far."
These events really provide a lot of social value to Yelp. Firstly, they are building community and good vibes in the site as a whole, and adding to the all-important "cool-factor". Secondly, the events are helping to develop strong offline micro-communities through building connections between individual Power Users in a specific location. Thirdly, the events also provide users with an incentive to post and be active on the site, so that they can join the Elite. Finally, the events provide Yelp with a great marketing tool, they can talk about the events on their blog, post up photos on flickr, and gain total notoriety from explicit photos taken at the Yelp Elite Mixers.
So, if you want your site to be cool, think about running events.