In my white paper on Enabling Web Services, one of the principles that I proffer is "Cool URIs Don't Change" (which, of course, is the title of a paper from Tim Berners-Lee). The larger point, however, is that URIs should be carefully designed, not just haphazardly thrown together. I just discovered a paper by Jon Udell from September 2000 called "The Art of Organizing Search Results" which makes the point even more strongly. Pay special attention to the second page of the article where he describes a de facto API for the Oreilly web site that was created inadvertently simply by choosing the URI conventions with common sense.
There are some that argue that URIs are a bad place for meta data, but it certainly is effective. People who believe this are probably the ones who are responsible for all those unreadable URIs you see created by content management systems. This has led Brent Simmons to coin his Law of CMS URLs: the more expensive the CMS, the crappier the URLs. Every day Utah's web API is being modified, built-out, and expanded as people add content. We must ensure that our URIs are designed carefully and usefully. To do anything else is to squander an opportunity to build something now that has lasting value.