The Magic Kingdom's Main Street USA will be closed for much of Thursday to host President Obama's official visit. It is expected that Main Street will be closed from park opening, through to the conclusion of Obama's visit, which should allow the normal parade route to operate at 3:30pm. Guests will be directed to other lands in the Magic Kingdom via backstage areas.
The event is White House invitiation only, so if you are planning to attend, it would seem unlikely that you will be able to see the President or the event itself.
To provide additional entertainment, Disney's Hollywood Studios will be performing 'Rock the Night! Fireworks Spectacular' on Thursday night at 7pm. This is not a regularly performed show, so is a rare chance to see a firework show at the Studios. Additionally, evening Extra Magic Hours have been added from 7pm to 10pm, and also at Epcot from 9pm to 12am.