First, for those who have never used a Fastpass before will be a brief explanation of what Fastpass itself. Each person who enters the MagicKingdom, EPCOT, Disney’s Hollywood Studios or Animal Kingdom will automatically get access to Fastpass by using their entry ticket. This applies to all passports, as well as annual passes. Using your ticket to get a Fastpass you will then receive a ticket that has a special 'window' of time in which you can use your Fastpass. This allows you to enter a special queue during that time to bypass the majority of the other line, which is called the standby line.
The time window on your Fastpass is a two hour window. You cannot use your pass before the first time in that window, but once a pass is issued, you can use it anytime after your window opens up. Say for example that you get a Fastpass for SplashMountain, and your time window is 1:00 - 3:00. You can then use the Fastpass anytime that same day after 1:00. It is also important to note that you cannot get another Fastpass until 1:00, which is the first time in your two hour window. Now the exception to this is that sometimes your two hour time window won't be until much later in the day. Say for example you get a Fastpass at 10:00 in the morning, but the time window isn't until 6:00 that night. This doesn't mean you can't get another Fastpass before then. Instead, you have to wait two hours to get another Fastpass, so you can get another one at 12:00.
Each of the four parks at Walt Disney World operates independently. If you are in the MagicKingdom at opening, and get a Fastpass where the window doesn’t open until 2pm, and you go to Animal Kingdom before that time you can still get a Fastpass there.
Here are the attractions at Walt Disney World that have Fastpass at each of the 4 theme parks:
The Many Adventures of Winnie the Pooh
Peter Pan's Flight
Buzz Lightyear's SpaceRangerSpin
Stitch's Great Escape!
It’s Tough to be a Bug
Living with the Land
Honey I Shrunk the Audience
Disney’s Hollywood Studios:
Rock ‘N Roller Coaster
Voyage of the Little Mermaid