Patrick Altoft is the Director of Search at Branded3 and he wrote an article today about Google making it harder to migrate to a new domain. From the article:
Changing domains has never been something to be taken lightly but in the past year, Google appears to have made it tougher for brands to carry out a legitimate re-brand, or domain change for other reasons, without suffering catastrophic SEO losses. We’ve been talking to a number of businesses that have changed domains and lost huge amounts of SEO visibility, even after doing some of the things that are usually recommended during a migration. It seems that Google has got a lot stricter recently when it comes to deciding whether to transfer trust and authority to a new domain. Unless you execute the migration perfectly (which big brands dealing with lots of issues and constraints often fail to do) you run the risk of having a disaster. Any issues that can affect trust and authority such as lingering unnatural link messages or duplicate content/page bloat all come into play during the migration and it seems that if you combine one or two of these issues with not redirecting every single page to the relevant new page, Google will not pass full authority through to the new site.
Make sure to the read the whole article as Patrick has used some charts to illustrate how some sites have been affected.
This is something that Elliot Silver could probably comment on as he has done what is probably the biggest rebrand in the domain content space. Moving from Elliotsblog.com to DomainInvesting.com is something he has written about and hopefully he can also comment here on the article from Branded3. Matt Cutts has done a few videos on the topic but not recently, so maybe things have changed.
Here is one Matt did a few years back.