Can I build the sage documentation in parallel?    
   I think this must have appeared on one of the sage mailing lists, but I can't find it.  Is there something like the -tp or ptest flags for building documentation?
 
 
I don't think so... but it's silly not to, if possible. You should check out whether Sphinx has this capability.
http://www.mail-archive.com/sage-devel@googlegroups.com/msg41177.html seems to say no, but that was half a year ago..