Once upon a time, I posted this classic: On Like Usage, which briefly shot Invented Usage to the top of search engine results everywhere and sparked a most interesting debate about the meaning and usage of "like."
As I draw close to the conclusion of my first actual syntax class, I have a few more tools with which to discuss 'like' and why it illustrates a challenge to the contemporary study of linguistics.
Categorial Grammar (CG) operates on the assumption that we can tell what type of word we're dealing with by where it's found in relation to other words. That is to say, we know 'ran' is a certain type of verb because it follows a noun phrase and provides a sentence. Another way to think of these relationships is as input-output functions. 'Gave' requires three noun phrases as inputs, and then provides a sentence (or, more accurately, a truth value) as output.
in the post linked above, I illustrated the myriad ways 'like' can be distributed throughout a sentence. it can modify nouns, adjectives prepositions, verbs... pretty much anything, now that i think of it. most linguists probably wouldn't consider this a problem, since they would claim that 'like' does not contribute to truth conditions. that is, that 'she went to the store' and 'she went, like, to the store' are true in exactly the same instances. if that's the case, 'like' doesn't contribute any meaning, and doesn't have to be accounted for in the grammar. linguistics adheres to a strict separation between language as a formal system (which syntax can describe) and language as it is used by people.
but 'like' DOES change the meaning, and in some cases the truth conditions (i don't believe they're the same thing) of sentences. it's one of many reasons why I think language use cannot be separated from language itself.
while syntax is interesting as an attempt to understand the patterns that arise from language use, the way it is actually implemented seems to forget that purpose. all linguists can do, at this point, is describe (to a limited degree) an idealized language that no one actually speaks.