The new FTC blogging guidelines are supposedly intended to go after the big commercial astroturfing campaigns, where publicity agencies pay large number of bloggers and tweeters to push commercial products. However anyone who blogs or posts to social networks needs to be aware of the rules, since it would be pretty easy to run afoul of them.
This raises significant free-speech concerns. Jack Shafer in Slate has a pretty good run-down of the issues: The FTC’s Mad Power Grab.