URL structures are a subject that most web designers ignore. You visit many websites that have a couple hundred characters in their web address (sorting mechanisms, session IDs and the like). URL structures are important because humans are much more likely to click on a URL they see in the search engine that reads example.com/information than example.com/2387/592837/babcarseat2352/information?ie=UTF8&node=165796011&pf_rd_p=328655101&pf_rd_s=left-nav-1&pf_rd. Not only that, but it is important for search engines to include your keyword in your URL.
I recommend that people use the simplest possible URL structure that they can make work with their website. Ideally, you would only have a one-level deep URL like example.com/tree-article. If you view my URL structures, they have a number at the end- I had to include the post number so that WordPress wouldn’t end up having two articles with the same URL. The number at the end of the URL structure is the post number, which is guaranteed to be unique. Other than that small concession to smooth site operation, my URLs are as simple as can be and are human readable. For example, when someone sees my site on Google or Bing or Yahoo, they can tell what my site is about by just reading the URL: joelx.com/how-to-improve-your-url-structure/3377.
URL’s that are shorter also get a higher clickthrough rate so for articles that I expect to gain a lot of search engine traffic I try to make them one or two words added to the end, such as joelx.com/demotivational-posters.