LJ::journal_base — Returns URL of a user's journal.
uuser. LJ::User object, user hashref or username of user whose URL to make.
vhost. What type of URL. Acceptable options: "users", to make a http://user.example.com/ URL; "tilde" for http://example.com/~user/; "community" for http://example.com/community/user; or the default will be http://example.com/users/user. If unspecified and uuser is a user hashref, then the best/preferred vhost will be chosen.
The tricky thing is that users with underscores in their usernames can't have some_user.example.com as a hostname, so that's changed into some-user.example.com.