You already have a mute button.. do you really want to deal with unplanned un-muting as opposed to planned muting?
I used to play eve online, having a few hundred people in a voice channel would be impossible if push-to-talk wasn't made mandatory.
It is very frustrating.
On GNOME I have set up a hotkey to mute my microphone (this is available but unbound by default). It is amazing as it works for all applications and doesn't matter what window is focused. The only downside is that you don't get the mute indicator.
If you are talking about the application-specific software mute, I had such a terrible time finding it amongst all my open tabs and latency every time I wanted to type or speak that I wrote the above hardware-ish button.