For me problem occured for the first time after kernel upgrade from 2.6.25-r7 to 2.6.29-r1 .
During shutdown system hung with message:
“Killing processes using ALSA”
There is bug for this issue and patch (working for me) here that’s needs to by aplied to /etc/init.d/alsasound (wrong order during module unloading)
I havn’t tested if this is fixed in alsa*-1.0.19