Go early, that's what we did in July 2010. We were staying at the Wyndham Beachwalk, reserved a car for the day at Enterprise. We picked it up like 7:30 am ish. I had ready how busy it gets, but when we left around 1pm ish it wasn't as bad as I had been lead to believe.
No problem getting on to USS Arizona or the USS Missouri. The kids really enjoyed it(9/13 at the time) ask when we are going back!
It's kind of like WDW, get there at Rope Drop and you'll be fine.