I can't wait for this movie, but I'm a really biased longtime Tarantino fan. As much as I would have liked to see Will Smith as the lead, I think Jamie Foxx will be more willing the push the envelopes that QT plans on pushing. Will Smith is more of a family man than a risk-taker, which is mostly a good thing (for example, Seven Pounds, I Am Legend). I will always approve of Christoph Waltz being cast in anything for any part, he is a magnificent actor. Leonardo Dicaprio has some serious acting chops, but this should be a stretch and a chance to prove himself to his non-believers.
As for casting his friends, I shamelessly have faith that Eli Roth could adapt to whatever small-yet-essential role that Tarantino will cast him in. Rob Zombie, though...that, I'm slightly nervous for.