Its not really an end, its more a goal. As far as I understand, when you defeat the dragon, you can take the portal back to the spawn point of your world (via a ridiculous "end credits" of sorts, which Yogscast brilliantly lampoons) and you just carry on as normal.
One thing I'm interested in finding out, is if all the strongholds lead to the same end and you can only fight the dragon once, or if there are multiple Ends and/or Dragons so you can do it over again.