As I pass the certification Spring, I give you a feedback of my preparation and of the exam.
I work all days with Spring at myjob, but also in my free time. I am Spring Leader on a French portal and I currently work on a contribution for Spring WS.
To prepare the certification, I followed the Core Spring training, to refresh my memory about the various topics under consideration.
I quickly read the official documentation one day before the exam, too.
The exam was more difficult than I though.
However most questions remain in a correct level that all good Spring users can answer. Other targets details that we find easily in the documentation or Javadoc, but that we do not know necessarily in head.
I passed the exam with 82% in about 50 minutes.
Hope this helps