julie yThe SeaWorld Christmas shows are only on select dates. For 2013, you can see those dates here: http://seaworldparks.com/en/seaworld-orlando/Christmas/Learn-More/Calendar. The Christmas Market (I believe) is open every day.

@Matt The reserved seating package is a new feature, so I haven’t heard any specific feedback about it. But, if it’s like most similar theme park offerings, it likely comes down to what your budget is verses the amount of planning you want to do. Having reserved seats will allow you to keep less of a rigid schedule when you’re on-site, so you won’t have to get to shows 30 to 40 minutes ahead of time, etc. 
If having a little more time to relax is worth the price for your family, it’s probably a great deal. If that doesn’t quite justify the price for you, then you can do just fine without it — as long as you have your day pretty well planned and you stick to a schedule.