The microphone on my Droid Bionic doesn't work on calls, Google search, or voice to text. It does work when I record video and when I do a voice to text, the phone is registering that it is hearing sound (mic icon flashes) but it does not write anything down. I've heard it's because a critical update hasn't been run, but I cannot find a way to check.
I'm not aware of any Bionic updates that have occurred the past few months, but you can check by going to:
menu > system settings > about phone > system updates
You also might try a system cache clear; that helps a lot of issues (it may or may not here, but is worth a shot).
Good point Tik on my Razr I had similar issues and I cured the issue by simply power cycling and as soon as my Razr came back on and settled I power cycled it again that what helped my little guy.. and make sure to check all your sound settings b33