Not 100% sure on the methodology here, but it's an interesting bit of research nonetheless. Researchers from New York University have said there is a definite link between new albums being discussed on credible music fan blogs and record sales.
Professor Vasant Dhar and former NYU student Elaine Chang monitored how often 108 different album releases were blogged about in the first quarter of 2007, and tracked their Amazon sales figures in the four weeks before and after release. They found that albums mentioned in more than 40 legitimate blog posts scored album sales three times the average, or five times average if they were major label artists. Albums that were blogged about over 250 times scored sales six times average. They said that high numbers of MySpace friends also correlated with higher sales, though the correlation was not as strong as with blogging.
Of course these correlations do not necessarily mean the blogging is leading to the extra sales - the extra blogging is probably a sign an album has a higher profile, and that profile will result in higher than average sales. However, it's all interesting nonetheless.