This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
I put 2 months into it, ~100 hours I am guessing. Solely used K&B SCJP book which was great. I tried to read the chapters more than once, and worked all the problems/tests as many times as possible. I saved the "bonus" mock (the one I downloaded from the publisher site) for last, so that I could measure where I was 2 days before test day.
I'd say K&B mocks are a good predictor of how you'll do on the real test. I thought the real test was a little easier than the mocks, but not that much easier. It's a good strategy to prepare as if the exam will be as hard as the mocks, so you'll have that margin of safety. I got 70% on the last mock so did slightly better on the real test (81%).