I first learned about Java while getting my Bachelor's degree, but at the time 1.6 was the latest version. I've had about 6 years experience in other OO languages since then (mostly PHP and some C#), so I was familiar with most concepts already. I just needed to learn the way Java dealt with them.
I first studied the subjects that are mentioned in the exam objectives that I wasn't already familiar with, and then took the foundation test. I was rather disappointed with that result, but I read all the explanations and available forum posts, read up on the subjects I still felt unsure about and continued with the next test. I repeated that process for each of the tests, and was able to learn the concepts quite quickly. Overall it took me just a month (full time) to prepare for the exam.
I felt the actual exam was a lot easier than the Enthuware tests. I think Enthuware tries to trick you in more subtle ways than the actual test. Overall I think it is a great tool for learning.
My notes are available at the Enthuware forum, link below (txt and zip files aren't allowed on this forum). They are mostly things I found odd or difficult about the language, and are in no way supposed to be a complete overview of all subject matter. Nonetheless, I feel they might help others prepare for their exams.
Next up is the OCP
Results of the Enthuware tests:
Foundation - 64%
Test 1 - 76%
Test 2 - 89%
Test 3 - 74%
Test 4 - 84%
Test 5 - 73%
Test 6 - 89%
Test 7 - 91%
Final test - 86%