McKinsey recently published the results of its second annual survey of social media [1] usage in the enterprise: 'Building the Web 2.0 Enterprise: McKinsey Global Survey Results'. (You need to register with the McKinsey Quarterly website to read the article, though).
The results, in one sentence, are encouraging: "Companies have adopted more Web 2.0 tools this year than in 2007 and are using them for higher-value purposes". For a good overview of and commentary on the results, read Hadley Reynold's article on this topic on the FASTForward blog.
[1] The term 'Web 2.0' is just plain silly. It's like saying: "We now ship frozen food in refrigerated trucks via our road network so we should start calling it 'Road 2.0' because that's an extension of what the network was originally created for. Regular warehouses are 'Roads 1.0' while refrigerated warehouses are 'Roads 2.0'." And so on.