Importance of URL Design for Websites?

Id love to get everyone's feedback on the importance of URL design in relation to overall web architecture and design.

But even more important, I'd like to learn some details:

    * If you DO NOT think URL design is import, WHY NOT?
    * If you DO think URL design is import, WHY?
      And If you do think it's important:
          o How do you define URL design?
          o Can you give examples of good URL design?

Thanks in advance for your input.

I'd say it depends on where you're going to use those URLs. If you're going to use them in printed form (ads, magazines, paper newsletters, etc.) then it may be more important to have short, easy-to-type URLs than if they'll only be linked from other HTML pages.

Another issue has to do with search engine optimisation (SEO). Using a good document name (and path names, where applicable) may increase your chances of being found for your relevant keywords.

A few things I think are worth thinking about:

    * Use short path names and document names if people are expected to type them in.
    * Use lowercase only, especially on servers that are case sensitive.
    * Avoid underscores in URLs, because they can be hard to see when the link is underlined.
    * Avoid spaces and non-ASCII characters.
    * Avoid query parameters, if possible. Use mod_rewrite or similar instead.