A test from Google Blogscoped indicates that 60% of all blogs hosted on Google’s Blogger blogspot.com domain are spam blogs.
The test of 50 random blogs found 30 of them to be rubbish. A later test by the site of a further 100 blogs on blogspot.com indicated a spam rate of 42%.
To quote Philipp Lenssen
“Google itself shows there are around 7,500,000 pages hosted on Blogspot. If we extrapolate the number, we might estimate Google is hosting 4 million spam pages. (Of course, this number is by no means in any way precise.) Even though I expected some amount of spam, I was surprised just how much it is. From the small sample I took it looks like on average, a site hosted at Google’€™s Blogspot is more likely to contain spam than anything else.”