The latest version of Photoshop CS3 Extended has a great new feature that allows you to automatically remove people from photos. It requires that you take multiple pictures using a tripod. Photoshop then uses the multiple pictures and creates a new picture containing only the elements that are the same from picture-to-picture. In this way, people and other non-stationary objects will be removed.

To use this new feature, you must first be using the Extended version of Photoshop CS3, if you don't have the extended edition you can't user this feature.

Start by taking several photos of your image using a tripod so that the image is the same in all the photos. I've found that 3 pictures is usually sufficient, but if there are a lot of people like you'd have at a major tourist attraction, more photos will result in better results.

Once you have your pictures on your computer start Photoshop CS3 Extended and select choose File -> Scripts -> Statistics. For the "Choose Stack Mode" option select "Median". In the "Source Files" section select your pictures. Finally, check the box next to "Attempt to Automatically Align Source Images". Click OK and Photoshop will start processing your images. It'll take a minute or so, but the results are excellent and the amount of work required is almost none, this is a great new Photoshop feature.