This was happening to me as well. The only way that I could type in the editor was to right click the editor so that the popup would come up and then it would allow me to start typing in that editor again. It would always happen when switching between files. I updated to 1.5 update 3 and that problem seems to have gone away.
Other JIRA Issues which I believe report the same bugs:
IDEA-1563
IDEA-1215
IDEA-1160
IDEA-1694
3316 on Linux is eating my key strokes in the editor and not displaying them {:-)
OK I just downloaded JDK 1.5.0_03 (Update 3) which was just released today. It resolves all my problems !
This was happening to me as well. The only way that I could type in the editor was to right click the editor so that the popup would come up and then it would allow me to start typing in that editor again. It would always happen when switching between files. I updated to 1.5 update 3 and that problem seems to have gone away.