Quite impossible to open a magazine or a web site without an article about social media / community. Rules are definitively changing and that's, for part of it at least, a good thing. Brands feel that something is happening there but most of them don't really know yet how to use it mainly because it can be extemely tough to accept to loose control and let people interfere with your brand. It means that you need to be very good and transparent on what you offer, your values, otherwise it will comes back to you. What's definitively scary for companies is that they realize they don't really have a choice. Ads are part of the process to catch new custumers but are eventually a small part of it.
The main difficulty is probably that now more than ever, brands must EARN their audience, customers or whatever you call it. It becomes quite impossible to just send a message away. Brands must interact and it means being good ! Everything they do is under the eyes of their audience.
One of the key for companies is probably to create a strong link with their customers threw social communities. Now, once you've said that, you've said nothing. The all point is to know how you push people to enter Brands's world on social communities. To catch a "fan" on Facebook has a great value because the "catched" is now captive. Let's be clear, that's a dream for brands, right ? No ad campaign can bear the comparison.
There are at least two ways to attract people on your "fan page" :
1) Values of the brand - so high that people will want to be associated with it ( a transfer - "Look at the brand I like, it will tell you what I am or what I'd like to be")
2) You offer value - via vouchers for example. If you become a fan, you'll get special offers, rebates, exclusive informations ...