The specific issues known at this time (spring 2013) are:
<ul>
<li>a bug in PulseAudio that causes it not to give up the
- soundcard when JACK asks</li>
+ soundcard when JACK asks (<a href="https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/1163638">LP: #1163638</a></li>
<li>bad package dependency information that causes a critical
package to be missing even when JACK and PulseAudio are
installed</li>