I posted this last week so please forgive the redundancy, but I truly am passionate about 4 in 1 days.
I'm a California native, lived and worked at Disneyland but had never the opportunity to go to WDW. Last April, 2013, I had a biz trip in Orlando. I had one day off and a parkhopper. With no foreseeable future plans to be back, I wanted to see all 4 parks "meaningfully" and as a newbie, that meant not missing much of anything. Of high importance to me was to see all the bigs that are in DLR to compare, to see all those that are no longer in DLR (for nostalgia's sake), and to see those amazing things that only exist in WDW - so pretty much everything.
Nope. Thanks to TP, it worked like a dream. 13.2 miles of walking and 14 hours later, I finished my goal and even got to ride Jungle Cruise (my fav) one more time before closing.
A big part of my success was navigating the transportation system. We've got nothing like that in Anaheim so it was totally new to me. I played out every transportation scenario with the transportation wizard (http://www.ourlaughingplace.com/aspx/twiz.aspx#.VCXC_CldWn5) and found that the shortest amount of travel between 4 parks in 1 day (while still saving MK for last to take advantage of the most meaningful night time stuff - MSEP, fireworks) is found in AK to EP to HS to MK.
And then I stuck to my plan like a drill sgt. When BTMRR went down, I optimized again and followed the plan.
It was amazing.
One thing to note is that I think another factor was that I was alone. I think I could maybe do it again with a second person, but he/she would have to be just as passionate and serious about hitting the important attractions so as to minimize rests and potty breaks.
I watched as several determined groups of younger people than myself charged forward toward a goal, leaving me behind with my steady pace, got distracted and got slowed down by their own mass and community spirit. I always got to the goals before them.
I hope that's helpful.