Tell Us On Facebook - Like This - Friend Us
When you are asked to "like this" you're asked to add your name to a list.
When any business wants you to "friend" them, they're asking two things. First, believe that corporations should be the same thing as people (last time I checked, I did not have any major, multinational corporation that I could go play a round of thursday afternoon squash with at the racquetball court..). Second, they want to be able to see everything your mother sees - out of your profile.
The still-amazingly flat and largely ineffective security model in Facebook is designed for marketing departments to farm data from you. Although the site got its start in hatred, the ranking algorithms at the core of the site's basic code are designed not to deliver data to you - but to store data for a lurker. In that primary case, it was a disaffected young man who wanted to prove that his girlfriend was ugly.
Google plus is better, and its important to remember that your core login to Google is you (with your real name or nickname - they will ask you to prove that you actually use it) - but the public identity you can keep can be six , ten or even twelve degrees separated from public marketing robots. I am fairly convinced at this point that Google's motivation is not evil - although whatever you leave out for those robots, I'm pretty sure they can use.