>> As a member of the generation that uses this like:
>> It is not actually freestanding - a grammar has evolved of when it is and
is
>> not used.
>In particular, it is used as a marker of indirect and sometimes even
>direct discourse: standard "I said that P" comes out "I'm, like, P."
I actually find that usage less commonly than as a marker of secondhand
knowledge, but it is used also.