I took the exam in April and October of 2010. To be honest, I thought I did better in April than when I walked out of the room in October, but luckily I did pass the October Exam. I took a small course and studied only water type problems, and failed the test. In October, I took a different course, designed on all aspects of the test and passed. I probably put in around 250-300 Hours each time. I tried to keep up with the time, but about half way through the second time, I quit tracking it (it stressed me out).
I would suggest that you look at the different tutoring places out there and see what is best for you. Personally, I did envpetutors.com. They send you the material and then talk to you a few times a week. I liked the setup they have.
Definately buy Metcalf and Eddy's Wastewater Treatment Book (Volume 4) and Cooper and Ally's Air Pollution Control Book. Those are great references for the exam. Also it will not hurt to take in Lindburg's book if you are familiar with it.
Good Luck!