I think the timing will help you a lot rather than just trying to notice punctuation. After all, music is about the rhythm.
I completely agree though, the metre/rhythm plays a huge part in a poet or rapper's flow and you don't get the full story without incorporating it. The issue is that I haven't found a way to programmatically pull the metre from a song, and rapper's don't generally keep track of their metre, let alone put it online in a machine readable format (though I'm sure you could find ones for hugely popular songs like 'Lose Yourself' online!).
I am interested in figuring this out though, and have been throwing around ideas for people to simply generate metre for songs by having a tool that simply allows users to match words to times in a song. Though I'm not sure how scalable that is, or how to create such a tool that is drastically simple and fast to use, because otherwise it defeats the point. My hope is that there'd be a way to algorithmically parse the audio and look for inflection points in a song for where words might lie but I've done no research towards that end. digression: This kinda tech would probably be useful for generating 'sing-a-longs'
That said, I'm not sure how fine-grained karaoke systems get - whether they just display the lyrics for a whole bar of the song and linearly interpolate between the start and end, or whether they are a bit more intelligent than that.
Just a thought!
A utilty for finding and exploring internal rhyme schemes in poems and songs. I made this in order to better show people just how complex a rap artist's rhyme combinations can get. This was created with CMU's pronunction dictionary (http://en.wikipedia.org/wiki/CMU_Pronouncing_Dictionary)
The screen shot shows a subset of the rhyme combos found in the Eminem song 'Lose Yourself'. You can view my work in progress online at http://reasonedrhymer.com (Click on a combo or word to filter the results)
What I wanna do eventually: - Permalinks to analysis for specific songs (and which current combo's are being viewed in that song) - Speed up the core algorithm - Allow people to add new words to the pronunctiation dictionary - Move away from the barebones bootstrappy look - Explain the process visibly on the site