I’ve recently started using Google+ Hangouts. One problem that I noticed out of the gate is that the Google Talk Plugin (which is required for Hangouts to work) thinks that it’s smarter than I am about adjusting my microphone level, an constantly adjusts it. This leads to the unfortunate side effect of everybody listening to my keystrokes. A little bit of registry hackery fixes this problem.

[HKEY_CURRENT_USER\Software\Google\Google Talk Plugin] 
"audio-flags"="1"

For the record, my default value for that key was 15.