Facebook and LinkedIn derive their value from being “networks of trust”. The whole point of personal networks like LinkedIn and Facebook is that they’re personal. We expect that a certain amount of the regular email we get to be spam, because such email is “public”. Anyone and everyone can (and does) email us that way. LinkedIn and Facebook are far more restricted. It is possible to send a message to someone who is not a contact, but it’s difficult, and you can only send one such message at a time. Your friends, however, have given you permission to include them on mass emails, because they trust you not to spam them. The value of your network is directly proportional to this level of trust.
Social Media is about reputations. Even if someone chooses to remain anonymous (and on LinkedIn, they never do), they're still identifiable by their relationships with other people and can be held accountable for their actions. This accountability is part of the reason why social media is such a popular venue for finding employees and service providers: usually you know someone who knows the person (or knows someone who or knows someone who knows the person) and can advise you about them. Also, as in the case of real life, reputations are contagious. A person who is connected to someone who is very trustworthy or influential (for example) is a more valuable contact than someone who is not.
Also worth noting is that Facebook and LinkedIn (especially Facebook) have "network update areas" for alerting your friends about your activities, and this is generally used for keeping abreast instead of email. If you send email to someone through either of these services, it's assumed you have something personal and urgent to say to them. This makes mass-mailings especially sketchy.
In general, the ideal LinkedIn or Facebook email should have the following qualities:
- Appropriate – Your message should be suited to whomever it is you are writing to.
- Useful – Your message should provide significant value. An opportunity to take your new seminar (for only $299.99!) is NOT “significant value”.
- Altruistic – Network membership is about being a team player. It’s okay to ask for favors for yourself sometimes, especially, if they’re the sort of favors that network is meant for and your friends can reasonably expect you’ll reciprocate someday. (“Help me find a job” on LinkedIn, for example.) But in general, it’s best to avoid sending emails that are obviously only for the benefit of yourself. People are not stupid, they tend to be more trusting of people who exhibit altruistic behavior.
In conclusion: Social networks like LinkedIn and Facebook are more personal than email and should be treated as such. In general, it's helpful to think of these sites as a private cocktail party. We have all had the experience of attending a party where someone took advantage of the cozy environment to push their pet charity, business, or fund raiser. Don't be that person! If you abuse the trust of your network, not only will you earn a bad reputation, but you will make yourself a liability to the reputations of the people who have vouched for your character by choosing to be connected to you.