I've always seen online social networking tools as extensions of what is done better in person, and a pretty good substitute for when it's just not practical to be in person. This goes back years and years, to online forums, prodigy (remember that?), etc. If you think of your participation online as much like an in-person event as you possibly can, you'll benefit the most possible.
Say, for example, if you attended a talk at a conference, and you gained a lot of useful knowledge from it, and then found your self face-to-face with the speaker right afterwards, you'd say "thanks, I learned a lot from your talk". And if you were sitting at lunch and someone said "Do you know anyone here who can help me with an SQL issue", you'd point them across the room to where your favorite SQL expert sat. Or, you'd do your best to answer the SQL issue yourself.
What we're thinking is that perhaps if we picked a day and asked everyone to speak up in just one small way, we might get some folks more comfortable with participating online, and everyone would benefit - make some contacts, get some questions answered, reconnect with someone you met in person, etc.