Monitoring blogs bears absolutely no resemblance to any aspect of recruiting and running HUMINT sources. It also does not require the manpower effort of the old FBIS daily translations of hundreds of foreign media sources. Let's not overblow the task.

The key word is monitoring. It doesn't even require reading the entire contents of the blog/journal/forum. Software identifies and highlights new content for you (text, images, video), then all that is required is to gist through to find and follow up on the bits that are of value.

For monitoring and data mining purposes, there is no "working in" required. Even where access requires registration and membership, most of the sites in question do not have levels of restricted access by post count etc. Simply register and you're in. The major difficulty is language - many sites where there is true value to be mined are not in English. And when dealing with the slang and abbreviated terms used in web postings by the indig, success in collection is far more likely when you have a native speaker working for you.

Now, if the idea is to take a step further, along the lines of LE efforts to catch child predators by posing as young'uns in internet chat rooms, then yes, it will take a much larger effort tightly coordinated with other intel elements. That is another discussion entirely....