A post from Strategic Marketing Montreal discusses the implications of using a 301 redirect within Google. Apparently, a specific domain changed, but fortunately, the 301 redirect worked so well that there was no drop in rankings.
This blog has just moved and the good news is that the move was done in such a way that the Google visibility was maintained unchanged throughout the move.
Interestingly, though, the site 2 results in the SERPs. One shows the old URL and the other indexes the new URL. Of course, if you click on the old URL, it immediately shows you the new site, but it's still being indexed for the time being. At Sphinn, Barry Welford suspects that this observation will change as Google fully acknowledges the 301 redirect.
The more intriguing thing is that, despite the 301 permanent redirect, both the old URL and the new URL show in the SERPs. The redirect was put in place 6 days ago. My working hypothesis is that the old one is not de-indexed but eventually will sink without trace.
Ian aka g1smd expounds on this idea and says that 301s can hang out in the SERPs for a good period of time:
The old URL will take up to a year to drop out (though that time scale seems to be reducing with each new Google advance). It will likely languish in Supplemental for most of that time. That is NOT a problem, as your on-site redirect will deliver the visitor to the correct content at the correct URL anyway.
Either way, it's not a problem, and it's interesting to see how 301 redirects work with Google.
Forum discussion continues at Sphinn.