I've been seeing this a lot lately and I must admit not knowing what it was.  Why would you say "Long Live" something if you just said that it's dead.  I searched google and discovered many interesting ones.  The blog.  The web.  The powerbook.  Economics.  Devo.  HTML.  Then I saw one for "The King" and I thought to myself, That's gotta be it. 

Thankfully it was, and my reward for searching it was this wikipedia entry, which basically states that it was a proclamation orated upon the death of one king and the succession of another.  So I guess an older powerbook dies and is replaced by a new one?  And I suppose Devo split up and a new Devo got back together?  And Web 1.0 is dead, so long live web 2.0.  Interesting.