How to make microphone work [solved]
Here's a hint for people having trouble using the microphone:
I'm using Internet Explorer on Windows 7. My microphone didn't work, even though I had:
1) enabled the microphone on the Duolingo account settings page (http://www.duolingo.com/settings/account).
2) enabled the microphone and camera in the Flash preferences applet (http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager06.html OR right-click on the Record button, choose Settings->Allow/Remember).
Those two steps should solve it for most users. But with my Dell Precision, I had to do one more step: set the "default device" for sound input. Go to the Windows Control Center -> Hardware and Sound -> Sound, you see a window with four tabs. The second tab is "Recording", and I had to switch the Default Device from "Microphone/Line In" to "Microphone Array" (that's what's built-in on my laptop).
If your setup requires different steps, post them here for others!