Is Valley Girl speak "like", entering the language?

First of all, I want to acknowledge that Kosmonaut’s answer is a good summary of what is called “quotative like”—use of the word like to introduce a quotation. As he explains, it fills a unique role in English not easily replaced by other words.

However, what I wanted to note is there is a difference between quotative like and “filler like”. Filler like is the one that people frequently object to, where the word like is added without adding syntactically to the sentence. In the original question’s examples, only the first like (“So like, I had this teacher”) is filler like. In all the other examples, like plays an actual syntactic role. If you take it out, the sentences don’t make sense. The like added at the end of the question (“in like a literate context”) is an example of filler like, not quotative like.

I can understand objecting to filler like—it is a hesitation word like um or uh that adds nothing to the discourse, although presumably spoken unconsciously. But objecting to quotative like is more complex because although it is a new construction in English, it serves a specific semantic role for which no other construction can quite substitute.

I can't think of any other examples at the moment, but I can offer a few interesting comments.

The word like in the sense you are using it is a discourse particle to indicate a possible mismatch between words and meaning. This was first noted by Schourup (1985).

Compare the difference:

1. John said, "what are you, crazy?"

2. John was like, "what are you, crazy?"

Sentence (1) implies an exact quote from John, while sentence (2) is paraphrasing or giving the gist of his reaction — he didn't have to say those exact words at all. It can even be used to recount facial expressions or emotions, e.g. "and I was like (O_O)", where if you are speaking to someone you can mimic the facial expression of your story.

Note that, in the reference I linked to above, there are other uses for like besides this particular function.

I wish I could find a reference for this (and if anyone can find one, please add it to the comments), but it is well-known among linguists that adolescent girls are very often at the forefront of language change (and men are generally more conservative than women overall). So it is no surprise that something considered to be exclusively done by adolescent girls in the early 80s could be fairly widespread in 2010 and increasing.

As I mentioned in the beginning, like also provides a useful discourse marker that other words do not replicate, which means that it has linguistic value — it provides something unique. This leads me to believe that, once the valley-girl stigma is a thing of the past (who knows how long that will be), like will only proliferate more (unless something else comes along in the meantime!). Just think how far it has come even with the stigma in existence. People who think it is silly sometimes find themselves using it in speech in spite of themselves.

I find this word (and its viral power) fascinating.

For what it's worth:

"was like" meets an important need: a way to indicate that you are paraphrasing. I'm a 35-year-old English teacher from the UK, and I sometimes spot myself using it. Before "was like" found its way into my active vocabulary, I had to resort to such clumsy expressions as "He said something like ...." or "His attitude was all ...."

So, yes, I think "was like" is here to stay. Sooner or later, a well-spoken member of the British Establishment will blurt it out in a formal interview. Then, in their next convocation, the GCSE English teachers of the land will hammer out a proposal for "was like"'s correct usage, to be ratified in Her Majety's Most Gracious Speech at the State Opening of Parliament the following May.

In the US, you'll know "was like" is acceptable when you see it in a Supreme Court judgment.

18 months later, my thinking on this matter has changed a little.

Compare these sentences:

John said, "Yeah, what about it?"

John was like, "Yeah, what about it?"

John asked why I thought this was important.

John was prickly and defiant.

The first is simple, direct, and correct, but isn't suitable if the speaker is loosely paraphrasing John.

The second is simple, direct, correct, and is suitable for loose paraphrasing.

The third doesn't work, because it describes the content of John's statement, but the speaker wants to convey John's attitude.

The fourth works, but it lacks the dramatic impact of portraying John saying, "Yeah, what about it?"

These are quotations, and the article clearly wants to convey the youth and enthusiasm of the speakers, by demonstrating to you how they communicated what happened in conversation.

By analogy, what if this had been a TV documentary:

Option 1:

(semi-meaningless imagery; e.g. slow motion of crowded street)

Voiceover: Sanz observed that people did not know how to define curiosity.

Option 2:

(Interior, Sanz' office)

Sanz: People were like, Curiosity: Hmmm, how do you define that?

The first option seems to convey the same meaning, but the second tells you more about the kind of man Sanz is, and gives you insight into the way the discoveries were made.

This is how people talk. By definition, it has already "entered the language".