One huge problem in a standard Ubuntu install is that not all programs are actually using the PulseAudio daemon but instead still use ALSA. This is especially true with the flashplugin. Since PulseAudio and ALSA can’t use the hardware device at the same time, they block each other which leads to hangs and maybe even crashes of programs (e.g. browser).

The fix is relatively easy and consists of telling ALSA to use its pulse plugin for output - which routes the sound to PulseAudio instead of directly to hardware. It is explained at pulseaudio.org.

Basically you only have to create a file /etc/asound.conf with these few lines:

pcm.!default {
    type pulse
}
ctl.!default {
    type pulse
}

This tells all ALSA apps to use the PulseAudio output by default. Some notes may also be found on wiki.ubuntu.com.

You should also check that you have installed libsdl1.2debian-pulseaudio instead of the -alsa one.