1) A comparative phrase meaning "possessing no great dissimilarity from, but not neccesarily possessing similarity to."
That subtle denotation escapes most, and it is most commonly used as:
2) a clumsy, noncomittal way of expressing simple similarity.
1) Well, yes, I guess it would be fair to say that Bush's appropriation of power for the executive is not unlike the administration of Hitler's Germany, but that misses the point.
Taking back your approval of something that's been said or done, or something posted online.
This term originates from Facebook, where you can publicly say you "like" something, and then have the option to take the "like" back. "Unlike" does not mean you dislike something.
"I really like the shading and texture on this picture you drew of a man in a prison cell. Oh wait; the man is supposed to be me. Unlike."