This is for all my client friends who aren't sure which social media channel to use for what.
Facebook is strictly personal. It requires a deeper level of interaction to participate and shape any conversations that are already going on. Keep in mind that the parameters of those interactions keep changing. So stay updated on Facebook's latest rules & tools.
Why do we need Twitter when we already have email? Because email takes awhile to arrive. Twitter is instant. It's 1 to 1, making it the perfect place to offer on-the-spot expert advice, share time-sensitive deals, track what's going on at an event, respond in real-time to customer service issues or in crisis situations.
Linkedin is the be all and end all of professional networking sites. So use it accordingly. Make new contacts. Start a group. Ask and answer questions. Conduct informal market research. Post job openings. Or get creative and tap into "life events".
Many clients use YouTube to share brand content. A word to the wise, unless that content is hilarious, or ridiculously useful, keep it on your brand site. Instead, use YouTube to let your customers create their own videos. How do you get them to generate content for you? You don't seriously think I'll give away all my trade secrets... Ping me and I'll hook you up. :)