I've been using Mavrix diligently since DP1. Even after DP8 there are still lots of issues/quirks that need to be ironed out. I really doubt the GM is near and I suspect Apple is behind schedule (thanks to iOS).However, if they do release another DP, things are looking bad for an October release of Mavericks and thus for the rMBP.
So, fingers crossed for no more DP's!