I've lived right outside DC for most of my life. Worked in a lot of highly secure locations (including the White House). Since I've been a member at my church, every President since Jimmy Carter (except Pres. Obama) has visited on a Sunday at least once. President Reagan dropped by my high school once. Even got to shake President Obama's hand this past Monday while doing some volunteer work at a DC school. And most folks around DC have been caught in a President-induced travel delay at least once. All that is said to give a little background on what can be expected.
- As others have stated, an advance group from Secret Service has been working this onsite for at least a week. Every doorway, rooftop, window, manhole cover, and trashcan will be checked, and access to them will be restricted. I imagine that the Utilidors will be exceptionally difficult to navigate, if not shut down completely for a good amount of time.
- I would think he will take Marine 1 from the Airport to WDW. They (and there are always several of them so they can play a shell game while traveling) will make life much easier around town (for both the President and locals). It's much safer for the President as well, since securing every road is much more difficult (for everybody). If he does drive all the way there from the airport, prepare for significant road delays all around town and throughout the resort.
- In case anybody thinks this would be a fun time to stand in a crowd and yell something at the President, or make a joke to the guy standing next to you about a bomb, don't do it. The Secret Service has extraordinary powers to do almost anything they want to you for the smallest of reasons.
- I wouldn't be surprised if the Secret Service was monitoring threads like these on the bigger Disney-related sites to see what people are saying.