Subtle changes in iOS 4
Apple has made a big deal of many new features in iOS 4: Multitasking, Backgrounds, Folders, iBooks, etc. But some features, and general changes, they have said nothing about. Here is a list, nowhere near complete, of "hidden" changes. Feel free to add your own.
1) Airplane mode
2) Text passcodes
3) Lock screen background changes to current song if iPod controls are up, regardless of playing status.
4) Mac-style 3D Dock
5) Spotlight Search the web and Wikipedia
6) New Calculator app icon
7) Shuffle button in album track listing
8) "Find Me" button in Maps app is now a triangle-like concave quadrangle, not a circle.
9) Triangle shape described above appears in menu bar during location-finding
10) Autofill passwords (MAY have been in 3.0, but I don't think so)
11) Search Bing
12) In app store, a "+" appears next to apps that also come in an iPad version
There are probably many, many more. Apple said there are 100+ new features. If you find more, please post a reply.