Stuff I learned the hard way:
If journals aren't updating, make sure qbufferd.pl is running. If it isn't, remove var/qbufferd.pid if it exists, and restart bin/qbufferd.pl.
You need to edit the first few lines of cgi-bin/bml/scheme/global.look, since it doesn't (yet) respect the settings in ljconfig.pl. You probably also want to edit htdocs/inc/email-welcome.
The source tarball doesn't include images, so all your images will either be broken or loading from img.livejournal.com instead of locally. I nagged Brad and he provided an image tarball. Download it and unpack it in ~lj/htdocs.