Here are some common issues you might run into as you transition from Xcode 3 to Xcode 4.2.
- Quick Look at Xcode4 - the various window/frames, and some shortcuts for getting around
- No Editor - you might run into this when opening old projects in Xcode4.
- Add to Project - how to add files to your project
- armv6 / armv7 Issues - how to build your app so that it runs on older iPods and iPhones (the old armv6 architectures)
- Viewing Build/Run Logs - Xcode4 has a tiny debugger/log window at the bottom of the screen, but there's actually a better way to view these.
- Setting "MyCompanyName" in Xcode4 - even if you had it set before, Xcode4 handles this differently.
- Building Apps for Distribution in Xcode4 (and submitting them to the App Store)