Everything else went into folders named using two approaches: according to what I want to do when I pick up my iPhone, or what the app is designed to do. Some of these are obvious, like Games. When you create a folder, iOS 4 will try to name it for you. It came up with "Social" when I dragged two apps together, and as much as the word chafes, I haven't come up with a better option. Into that folder went the Phone app (this will seem logical to many of you and crazy to others, but the truth is I rarely use the Phone app, so I don't need it visible) as well as the Messages app, BeejiveIM, the Contacts app, Ping, Textie, and Birdhouse.
I would have put the Twitter, Tumblr, and tumblr gear apps in there too, but I use those more frequently. At first I thought about leaving them in the folder and giving myself some empty space on the home screen, but ultimately decided it made more sense to take out my most frequently used apps for faster access. Then it was just a matter of arrangement.
The top row is how I've had it for as long as I've been able to set the order. Yes, I placed "Find" under the Maps app intentionally, and "Utilities" under the Settings app because my fingers are already used to reaching there when I want to find something. Ditto for putting the Photos app right above the camera, since I often launch the camera when what I really want to do is look at a stored picture. 1Password went right above Safari because they too are linked in my brain, and Twitter, Tumblr, and tumblr gear wrapped around the "Social" folder to make a nice little "zone" where related apps are together.
Bottom right is the fastest place for me to reach when I unlock my iPhone, so I put the camera there. I can no longer use the "double click the home button to launch the camera" setting (iOS 4 reserves that for launching the "recent apps" switcher) which is a bummer because I've used that for as long as I can remember. I hope it won't lead to missed pictures of a certain high-energy 8 year old boy I know.
This is how I've organized mine; obviously each person will have to find what works for them, but I'm thrilled that I will no longer have to swipe pages or use Spotlight searches to find apps. All of them are no more than two taps away.
During my reorganization, I noticed something odd about moving apps around in iTunes. If you put a folder into the iPhone Dock while using iTunes, you can't drag any more apps into it. If you are moving the apps around on the iPhone itself, you can easily add them to folders in the Dock. In fact, that's how I did most of my sorting: I created four folders, put them into the Dock, and then swiped along each page, putting apps into them as I found them.