If you have read through the Tutorial you will have seen the article on Search Engine Friendly Urls and in the News and Comment section you may also have seen the article on Keywords in Urls. Here I am going to add some additional information and conclude with some practical advice.
From the results of the experiment we conducted in Keywords in Urls we know the following:
We also know there is research that shows url depth (e.g. slash-count) and url length (e.g. number of characters) can be used to improve some types of web search results. In addition a recent paper out of Microsoft Research, Web Search & Mining Group shows that the location (identification) of search terms (keywords) in the url can also be used to improve search results. The paper is not yet available to read on the web but for reference it is “Exploring URL Hit Priors for Web Search” Ruihua Song, Guomao Xin, Shuming Shi, Ji-Rong Wen and Wei-Ying Ma, Advances in Information Retrieval: 28th European Conference on IR Research, 2006. When and if it becomes available I will add a note here. (May 30, 2006 Dr. Wei-Ying Ma has kindly sent me a .pdf file of his paper which you can read here, URL Hit Priors.) I personally do not know if depth priors and hit priors (as they are called) are actually used by the three main search engines in their algorithms at the moment. However it would not surprise me if they were and if not now some time in the near future.
So from this and the previous articles the practical advice is that when constructing your urls:
This advice put into practice can be seen on this site