Corey Haines gave his Fast Tests talk at the Golden Gate Ruby Conference 2011 (http://confreaks.net/videos/641-gogaruco2011-fast-rails-tests), here's my feedback on it.
So first up, I think it's very interesting to see another take on how to speed up Rails testing. There's been a focus on it for a couple of years now with various solutions coming for it. From running tests in parallel, to tweaking the filesystem for faster access. Corey Haines take on it is that we should isolate ourselves from the framework that Rails provides and do as much as possible in plain Ruby objects and modules. In his talk he shows how he has been able to massively improve the runtime of his tests by implementing this.
I think it is a logical next step to the current that has been in the community for a while where we have been debating how to improve the design of Rails applications.