As Gregory pointed out, there’s not really an easy way to figure out your Flickr user id number. The only thing you can really do is take a look at the source of your photostream and pick the id out of the RSS feed address.
To remedy the situation I threw together Flickr idGetter, a little page that finds the user id for you. It essentially does the same thing you would, grabs the page, looks at the source and finds your id.