Contrary to Borgo's writup, like, as used outside the bounds of Webster's definition, is not just verbal garbage, meaninglessness tossed lazily into the middle of a sentance. Most teenagers could have told you this for the past decade or so, but for skeptics there's now a formal linguistic study on the subject -- an important study because linguists had previously assumed that filler-esque words conveyed no meaning, or, to put it more formally, that they did not change the meaning of a sentance.

Specifically, like acts on meaning in 3 important ways:

She's like five foot five.
She's five foot five.
In the first example, the speaker is indicating a general range of heights, centered on 5'5"; in the second, they're specifying a particular, exact height. In this case, like is synonymous with about.
She's like ten feet tall.
She's ten feet tall.
In the first example, the speaker is using hyperbole; the woman in question, though tall, is (assumedly) not actually ten feet tall. In the second, she is.
She was like, I don't see why that's necessary.
She was, I don't see why that's necessary.
In the first example, the speaker is quoting someone else. The second example, without the like, is mostly nonsensical. (Like is not exactly analogous to said here -- someone could say, "She was like" and then do that hand-snapping-across-face motion, or could paraphrase something said (perhaps in such a way as to comment on it). In both instances, the usage can be thought of as somewhat literal: what is being described is, in a way, what someone is like.)

This is an oversimplification, of course; like is in many ways a general-purpose meaning-softener, subtly altering connotations in a way that is difficult to deconstruct, and it can be used in innumerable situations (to cause oneself to appear less forward, for example). Borgo's transcribed exchange provides a few examples, but in general it's not a great guide; it looks like he's adding like where it's unlikely to actually have been said: e.g. "maybe I'd just be better off eating at like, home." I won't dispute that the word can be overused, but to dismiss any nonstandard use of it as annoying or useless is incorrect.

I read some general-media articles on the study a few weeks ago but I can't actually find any of them; search engine technology is such that typing "like" into one, in conjuction with whatever else, won't turn up anything useful. At least, not for me. Feel free to Msg if you find something yourself (or if you think I've left out one of like's neatly catagorizable uses).