What’s not to like about like? It’s a versatile word, but one easily misused and abused.
Like is a preposition: “He is like me in that regard”; “Like him, I fail to see the humor.” Take care to use me and us (and, in the third person, them), rather than I and we (and they) in association with it.
Like is also frequently employed as a conjunction: “Like I told you before, we’re running out of boxes”; “Like we’ve seen before, it depends on the situation”; “It looks like it’s going to rain.” However, this usage, once common, fell out of favor long ago, and it’s still considered a colloquialism that is out of place in formal writing. In each of these examples, as is the better choice. In addition, like is employed as a comparative term (“I’ve seen something like that before”) and is often seen as a substitute for “as if.” (“She looked like she might cry at any moment.”)
The word has overtaken the more formal — and, as explained below, slightly different — usage “such as” to make comparisons: “I prefer more dynamic sports like soccer,” rather than “I prefer more dynamic sports such as soccer.” The argument against considering like and “such as” interchangeable is that “such as” suggests inclusion (soccer is one of the sports the writer prefers), whereas like implies exclusion (soccer is representative of the type of sport the writer prefers but is not one of them). However, the indiscriminate appearance of either usage — and many writers, myself included, have used both in the same piece of content — is ubiquitous, and the interchangeability is unlikely to change.
Over the last few decades, the word has persisted as a filler, especially among young people (“I was, like, totally confused”), or — again, especially among younger members of the population — as a conversational substitute for said (“And he was like, ‘Go for it’”). I admit without embarrassment that although I am not young, I freely employ like in both usages — when I speak. In writing, I would use them only for humorous effect.
The first usage is adverbial, similar to colloquial usage like (I mean, “such as”) “It’s true, like enough” (as a substitute for likely). Other adverbial uses are as an alternative to altogether or rather (“All this time, I was calm, like”) or to about or nearly: “It’s more like a hundred dollars,” “It took, like, four hours.” (The latter usage is likely the inspiration for the use of like as an interjection.)
Like serves as a noun: “I’ve never met his like since”; “I have no patience with her like.” A similar usage is “the likes of”: “I hope we’ve seen the last of the likes of him.” (The sense for the latter usage, and the one previous to that, is often pejorative.) Recently, too, it has acquired the meaning of “something one likes,” such as a social-networking Web page. And, of course, it functions as a verb, meaning “To choose or prefer,” “to enjoy, or to thrive,” “to regard,” or “to want.”