First off let me say that I have used Intellij IDEA for years now and still believe it is the best IDE out there which is why I continue to pay for the new releases.
For the most part I have participated in the EAP releases since for the most part they have been fairly stable with some issues on occasion. I realize by definition it is EAP and with it comes risks of being unstable in certain areas but lately these releases have major core functional pieces broken. For example, Gradle not being enabled in the build so totally missing, GWT not capable of being enabled and Spring for the most part non-functional due to continuous exceptions being thrown. Now I'm having issues compiling a Grails project related to some stub generation which had been fine in the past.
I'm not sure what level of testing is done prior to the EAP releases but seeing how even a trivial test would catch some of problems I just mentioned I'm guessing not much. I hope this post brings some attention to the testing done for the releases. Even though this is EAP I don't believe that the EAP users should be performing the functions of what a QA team or unit/integration/functional tests should be doing.