There is a left-inflected tradition of cultural interpretation that casts laughter in a populist (if not necessarily marxist) frame. One might in fact go so far as to say that it is almost _left-wing common sense_ (for better or worse) to see laughter as almost inherently subversive and (if not quite radical) at least down-to-earth and popular (in the sense of belonging to people). So pointing out the power of laughter in itself doesn't add much to our knowledge at all.
Laughter often gets produced by practices of exclusion (excluding the object of laughter from the shared understanding of the comic and his/her audience) and inversion (overturning the traditional hierarchy of valuation). Exclusion as a mechanism of production of laughter is in itself politically neutral and, depending on the object and the context of exclusion, it can be reactionary or progressive. It goes without saying that racist and sexist 'humor' serves to cement the ties that bind the dominant group by virtue of its power to reproduce the shared understanding that casts out the subordinated as 'abject.'
Laughter produced by inversion, I think, may have a little more inherent progressive potential. M.M. Bakhtin's _Rabelais and His World_ is a well-known example of theorizing that explores this potential. Nonetheless, carnivalesque laughter produced by a temporary overturning of hierarchy is indeed temporary--a brief interlude that paradoxically confirms the order of things--though it may possibly show up the hollowness of the social order so inverted.
Laughter might be produced by the combination of exclusion and inversion of reactionary sorts. Think, for example, of straight frat brothers putting on a drag performance without identifying at all with women or sexual dissidents.
I am not interested in laughter per se, but I think it furthers discussion if we analyze various ways in which the comic can be produced.
Yoshie