The Q6600's we make at work have the SLACR spec number, which is the G0 stepping. We haven't made anything without it in over a month. As far as I can tell, since I personally handle thousands of these things on some days, is that they no longer will be shipping out anything but G0 stepping. Although unless retailers have some old revisions in stock and they want to sell them, but other than that, it's all G0.
Speaking of which, it's interesting to note the HSF that Intel uses. There's only three HSF they use, across the broad spectrum of products we offer. Just thought that would be interesting to share with you all.