Since Hardy Heron now uses PulseAudio as default instead of Alsa, some people might have some problems with it.
I was unable to hear the sound on a youtube video when playing a song or visa verse.
There is an easy solution for this.
You need to install “libflashsupport” using synaptic or enter this in a terminal
sudo apt-get install libflashsupport
That will fix that problem.
I don’t understand why it isn’t a dependency for flash, but well, maybe in the next release.