switch(date('md'))
    {
        case '0101':
            return '_newyear'; break;
        case '0323':
            return '_birthday'; break;
        case '1031':
            return '_halloween'; break;
        case '1225':
            return '_christmas'; break;
        default:
            break;
    };

You could change /path/to/theme to <?php bloginfo('stylesheet_directory'); ?>. (Or get_bloginfo() to return it.) This just makes things easier if you move or otherwise.

You're right, but you have to be careful about using it too much. It can't be used where I've written /path/to/my/side/pictures/directory/, for example, because that's an absolute path on the server. I also don't think it'll work very well in the included files.

Owen said on March 3, 2007:

I just pop a bunch of images in a folder… all I need to do to add more pictures is drop them into the folder.

You can read above at least two or three reasons why that solution would be limiting to me.