Great time of year to go there. You will love using your 17-55 IS there, I found it to be the perfect lens. I only used the 70-300 IS when I was on the safari ride at Animal Kingdom, other than that it was pretty much untouched. Below are two shots I took with the 70-300. The one of the Elephant I like as it make it look like I was hiding in the tall grass when in fact I was moving in a truck.
As for the fireworks shot, the EXIF is below.
Camera: 400D
Lens: 17-55 f/2.8 IS
Mode: Manual
Shutter Speed: 3.2 seconds
Apeture: f/9
ISO: 100
Focal Length: 23mm
Also below is some info from another post of mine talking about places to take good fireworks at Disney. Just keep in mind you will need a tripod, remote switch, etc. for good fireworks shots.
Magic Kingdom:
Approaching Cinderella's castle walking up main street go to the right of it as if you are walking to Tomorrow Land. As you make the turn immediately to the left is a Kodak Picture spot. About 45 min prior to the fireworks the Disney potog will leave and you can walk up to this fence and setup with your tripod. I was there two nights and not many people came up to the area, seems pretty unknown for watching the action. Some people will hop the fence after the parade is done, but they don't stay. Each night I was there only one family was next to me, plenty of room for a tripod.
I wish I had a pic to post of fireworks from this great spot, but the first night I didn't know we would be there and didn't have my tripod and the second it rained like a mad man and I didn't take my gear out so as to keep it dry.
Trust me though, with my 17-55 IS I could have framed the fireworks with the castle on the left and trees below if I wanted and still got all the action. Very nice location.
Epcot:
Go into Italy and you'll find a small Italian style bridge. Pick a spot anywhere on this bridge and you'll be all set. People don't go on to it until right before the actions begins so you'll be left alone to setup. There is an alcove right below it that would also be a great vantage spot but that is where most people hang out and in my opinion it is no better than the bridge and you won't have to fight for real estate on the bridge.
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