Please stifle the yawns--I won't go into KM in any detail. We all know the sordid history: employees take the most valuable corporate resources out the door when they retire, job to another company or even just change departments. The way to save all that "institutional knowledge" is to force them to pour their brain matter into tedious forms in -- ick -- intranet portals, and self-identify their areas of expertise.
Enter Facebook or LinkedIn, mix in a bit of wiki, some dog-earring, and a smattering of Twitter, and voila! KM disguised as banter and "what are you doing now."
Enter Mike Gotta's interesting discussion on the (failed) role of technology in fostering KM. He's right to say that people have focused too much on tools at the expense of profit.
Gotta, principal analyst with the Burton Group, also notes the entry of Oracle into the Web 2.0 fray. Interesting reading.