Down at SXSW they are chatting about (MP3) the Wisdom of Crowds - a book I really enjoyed. There is a key point in the book that gets drawn out over at Bokardo - it's as much about those who draw out the wisdom of the crowd as it is about the crowds wisdom. Take Google and their Pagerank algorithm as an example.
This notion has special significance for communicators. In a Web 2.0 world you should be monitoring and measuring those that are drawing out the dialogue as much as you and the media. For instance, what appears on Google News or Digg.
Next generation communications measurement systems will give you insight into - and weight accordingly - the "aggregators" of content. They will also start to give consideration to the conversations taking place on those sites. Take Digg as an example. Here it isn't just about aggregation, it is about the communities assigned weighting of that content and the associated commentary.
The new dimension in communications measurement will be relevance. Not as measured by abstract algorithms or as determined by communicators. But as measured by the wisdom of the crowd.