As $SUBJECT. or at possibly the protocol://domain part of the URL if lengthy URLs are a concern. just something a bit more descriptive than "Source URL" ;-)
Fixed in 20110915-1326
The TopicSourceUrl class gets a @PrePersist and @PreUpdate function called setTitle() that uses HTML Cleaner (http://htmlcleaner.sourceforge.net/) to download and extract the title from any source url that has an empty title.
The SkynetCommandLine Project has been updated with a method called fixURLTitles(), which has been used to update any existing blank titles.