What if there exists a system that goes out to all blogs, reads the comments, aggregates them into individual profiles. Each comment often has the name and website. A person shares her opinion at this blog, another one at another blog. Soon enough, you will be able to understand her thoughts. It’s a behavioral data mining operation.
Even more powerful, enhancing this with user-provided personal profiles (like from Yahoo, Google, Facebook, or something with individual data). At the end, you get a very powerful and invasive system. This idea would immediately raise a red flag for privacy advocates. Actually, I can’t think of any good application beside monitoring “suspicious” people, which already has a vague definition that could be, very well, anyone. Some big organizations, government or commercial, might already be doing this sort of analysis. Google is the prime candidate with sufficient technical capacity to perform such operations.