When you do casting of a LAN tournament, prepare.
Take a piece of paper and write an outline of your show. Get a list of players, get schedule, plan in advance what games you will be casting. Notice if there are any possible gaps in the schedule, think of what you may do during those gaps. Probably you'd want to interview some players, so plan that in advance - think of who you'd want to interview, think of questions you want to ask, meet players before the games and notify them that you want to have an interview with them after the game is finished.
Think of what you will do when there are unexpected delays. Let them be expected for you instead. Even plan on what topics you may discuss when there is a pause. Write down some trivia and stats, when you are not live, talk with players "backstage", get some cool stories from them, etc, etc. It all can be used when you have no action to talk about.
Think of who of pro players you would invite to cast with you and what games they should cast. Meet them before the games and ask them to come and cast, let them know beforehand that they are wanted to be casting games.
Think of how a random viewer experiences your stream. When someone tunes in at a random time, he should either see that something is going on, or he should instantly get an idea when things are going to happen. If there is a delay or pause, instantly put a message on stream telling when next thing is expected and always update it if something is changed.
Plan and prepare all technical features and organizational interactions beforehand. Get a test stream working a couple of hours before the tournament and test everything you can: caster sound, ingame sound, ingame config, switching between views, message display for users about delays or upcoming games, etc.
Basically, when you finally go live, you should already envision very clearly what your viewers will see in the whole 2-3 days of the tournament. It should be written on paper that you have before you. You don't have to put your show on strict rails, you should think of variations, you should think of what you can do depending on the outcome of crucial games, you should imagine all likely scenarios of the tournament and think of how you can present each scenario in the best way, but it all has to be pre-outlined and written down.
Then you will have most smooth, fluid and professional show that will provide your viewers with most pleasant experience.
Edit: just to avoid misunderstanding, let me clarify that this is just my general thoughts of how casting ideally should be approached, it is not necessary related to recent DHS'11 or any other particular tournament.