I just loaded the new jwm (dated 09/29/2011 - thanks for the update, curaga) and found that it was ignoring the tag
<Desktops count="8">
in .jwmrc and always giving me the default of 4 desktops.
By changing the tag to
<Desktops width="8">
I got back to the way it worked before.
Changing it to
<Desktops width="4" height="2">
yielded a rather nice little change.