In a sense, this would be a better outcome (for Lebanon's stability) than Syria or a Christian or Shia group being behind it. But it's too early to tell what this organization exactly is or what its aims are.
They also showed a short video clip with a young bearded fundie talking about the motives behind the assassination. He said that they targeted Hariri because of his relationship with the Saudis.
Update: Having digested this information over dinner, I think the tape Al Jazeera showed should be viewed with some suspicion. After all, how likely is it an Al Qaeda afiliated organization organized a 350-kilo car bomb to make a point about Hariri's Saudi connections? One interesting theory that I've heard (just a theory, mind you, no facts) is that Shias might be behind this, inspired by the example of Iraq, where the Shia majority has finally elected a majority Shia government. Worth keeping in mind, especially when you think that Hizbullah is also allied with Syria. (I should note now that Hizbullah has already condemned the murder.) Anyway, this one is likely to keep us guessing for some time.