I used P, A and S mostly on my D50 last month. I also used Manual for long exposure night shots because I knew what I wanted the settings to be and there is no possible way for the camera's meter to figure it out for me.
If I were you I would use P the majority of the time. This will allow you to change ISO as needed. Keep it on 200 during the day and anytime you use the flash. As it gets later in the day and there is less light or your inside and can't use a flash then you can move up to to 400, 800 and 1600 as needed (it may not always work, but at least your controlling the camera, not the camera controlling you).
If you want pictures of The Beauty and The Beast show at MGM and your to far away for the flash to work, then in P you can bump up the ISO to 400 or 800 and probably get better results. In AUTO or the other icon modes, the camera wont know what exactly your taking a picture of. It may or may not get you the right ISO.
If you want any specific type of depth of field then use A accordingly. (ie: you see a bunch of flowers you want to photograph, using f/3.5 or f/4 will blurr out most everything in your background, using f/16 or f/22 will get most everything in your background in focus. A close up picture looking from the bottom up of the guitar outside Rock N Roller Coaster, use A and set to f/22, you'll get more depth of field)
To get different effects of the many waterfalls at Animal Kingdom and other water features around the parks us S. A fast shutter, ie: 1/250 and up will freeze the water in motion. A slow shutter 1/30 (about the slowest you can use handheld) will give the water a flowing look.
These are just a few examples. Take them for what their worth. The beauty of digital is that you can see what you just took. If it doesn't look right to you, then try something different.