Cromdubh - I'm with you there. It's all oral tradition, isn't it?

Do you know, I've only just spotted this thread and have just seen the show to prove that the blues and rap mix absolutely fine so long as the person providing the blues element has wide open ears and the person providing the rap isn't one of the cartoon-cut-out gansta rapper bogeymen. Courtney Pine played at the Sage Gateshead recently and touched on so many forms derived from the blues, from straightahead 12 bar to bebop to hip-hop and he brought on one of the rappers from the band Faithless as part of his group - magical result of genuine fusion (not shotgun marriage crossover).   

Alternatively listen to Queen Latifah in Chicago - there's a rapper that could belt out the blues if ever I heard one.

BTW Billy - the practitioners might not recognise the term polyrhythm but that doesn't stop them from using such really effectively. Just like a lot of the blues guys who originated the form probably didn't express their ideas in the language of dominant 7ths and secondary dominants. But they still were perfectly able to play them. You don't have to analyse it to play it or rap it (something called talent seems to take care of that) but it helps to have the lingo if you're trying to make sense of it as a form.