This interesting article in MarketingMagazine reveals that Microsoft and LinkedIn signed a partnership allowing Microsoft Outlook 2010 users to access their LinkedIn account directly. Looks like Microsoft is really trying to enter the professional social network field! Time will show if this will have a significant effect on the market.
You can click here for a picture of what will be Microsoft Outlook Social Connector and its use of LinkedIn (which does not seem so great to me though!).