Apple never documents all changes to the iPhone firmware. Many bug fixes/polish never get a mention in the release notes. Unlike some more transparent software products, the iPhone firmware is a big secret. The notable exception is Safari, or at least WebKit. MacRumors has traditionally done a good job of documenting the undocumented and has a forum thread for 2.2. Here’s one I just noticed:
When updating an app via AppStore in 2.1 it would create a new icon in the last panel, download, then replace the old version. In 2.2 it now finds the correct app and overwrites it. As minor as this is, it’s a nice level of UI polish. Yet completely undocumented (publicly) by Apple.
I wish Apple would make detailed change logs available for everything they release. Separate from the traditional release notes. This would be a big help for anyone technical.