Customer Relationship Management

Put simply, customers do not want to be your friend.
Now, if you own a cult brand, your customer already loves you. But if not, a normal customer, even a loyal one at that, does not actively try to be your spokesperson. (By the way, did I mention how absolutely in love with my iPad2 I am?)  
A not so scientific, but a detailed scan through my friend's list and a thorough snooping through my friends' friends in my social network reveal that my extended network consists of roughly 4 categories of friends. As modern marketer you aim should be to get your brand into one of these friend circles and get your customer to advocate on your behalf to these friend circles.
1. The Cool ones - This includes my paleontologist friend from Denver who goes on fossil hunting expeditions from time to time or my pilot friend who moonlights as an urban landscape photographer.
Cult brands typically own the space for cool friends and it is difficult for every brand to attain this status. However, to gain new customers a brand needs to enter this circle of friends. Companies could always associate themselves with social causes and activities which its target audience considers relevant and attempt enter this space.

2. My Real friends -I hang out with them often, in the real or virtual world. We share similar interests, like the same brands and are outraged by the same things. I have multiple groups of such friends and they are mostly like me.
For a brand to enter this inner sanctum, it needs to be like me. The most compelling reason for a customer to want to 'friend' you on the social web is when this connection based on similarity in values and interests is established. This circle is the most powerful, as users unconsciously advocate on behalf of your brand. A quaint little Vietnamese restaurant in my neighborhood is frequent hangout of my friends after one of us had a great experience dining there and tweeted about it quite persuasively.

3. The Other friends - My acquaintances, I know them from school, college, previous workplaces. In my case, they make up for most of the bulk in my friend's list.
Typically an existing customer, loyal to your company, considers you in the 'other friend's' circle. Being in this friend's circle is akin to being part of the pile of unread mailers in a mailbox. Companies need to constantly endeavor to graduate into the circle of real friends where the customer can be actively engaged.

4. Family - To get into this circle you need to be family.  So, it is difficult to conceive that any customer would consider a corporation a part of this circle. However, the customer's ability to influence and persuade members in this circle is very high and hence a company could always market products and services specifically to this circle. Outside the social media, companies constantly market products to cater to one's family and similar promotions can be performed on the social web too.
To sum up, it is a well-known fact that customers prefer to give their business to a friend rather than a corporation. For a modern marketer in the present climate of the growing influence and popularity of social media, becoming a 'friend of your customer is the means to exploit this behavioral trait of a customer.
Adding a word of caution, if you manage to become a friend of your customer, you need to consistently act like one. As difficult as it is to penetrate into the friend's circle of a customer; the easier it is for the customer to de-friend you, if you start behaving like a business again.