Several of us found we couldn't edit in SQL Developer after installing version 1.5.

We could type alpha-numeric characters like SELECT * FROM SOME_TABLE, we just couldn't use any of the 'navigation' keys such as backspace, arrows, delete, home, or end keys. We found this issue on our Windows and Mac machines.

Here's the fix:

    Tools > Preferences - Accelerators - Load Preset...

    Choose 'Default' and click 'Ok' twice.

There isn't even any need to re-start the application.

(However, we still don't know what caused the problem in the first place.)