I think there are two sides of this "Like" feature madalion. On one side, you use it for showing affection or for bookmark purposes in regard to an individual post. On the other side, you use it to display your agreeing with the post(er) in question, especially during a heated discussion. Now, there is an interesting social dimension to it, which may quickly escalate to a 'social' lynch.
There is an unwritten rule which triggers a chain of events: If there are two different opinions clashing each other in a discussion, "Likes" count could determine the way where the discussion goes, especially if one of two opinion is controversial. What happens here is that silent majorty or so called 'lurkers' starts to Like the less controversial opinion, causing the Like count increase by the minute. When a new 'lurker' hops into the discussion, he/she would be affected by the sheer number of Likes one particular post received, just because of the fact that he/she would feel safe to be in a majority. Therefore, perhaps involuntarily and subconsciously, likes it. Others come and others like it as well. In a matter of seconds, the writer of the controversial opinion is socially suppressed, as it were, even though there may not be anyone who actually contributed anything to the discussion at all. By the sheer power of majority, that writer succumbs to yield.
Dubbed as a social feature, "Like This" phenomenon can be a handy social opression tool as well. Irony at its best, IMHO.