The S3IS lets you manual focus. It also has a nice sports setting for taking action shots and multiple shots in a row. And, of course, it dropped a couple of hundred dollars AFTER I bought mine.
I resized some pictures I took on a recent trip to DC with my wife and daughter. I hope they come out OK and give you an idea of what the S3IS can do.
Squirrel, full sized image.
Squirrel, cropped from above picture.
These are all resized to about 25% of their original size. I did it with MS Photo Editor.
My wife and daughter at the WWII Memorial.
This is a ram mount in the old Smithsonian building.
I call this one "holiday remembrance", it is a wreath laid at the Vietnam Veterans Memorial.