Cool URIs don't change.
One thing that's always bugged me is file extensions...I hate having to type ".php" or ".cgi" or ".asp" or whatever else just happens to reflect the server's implementation at the time.  If they switch from Microsoft to LAMP then their URLs will probably all break needlessly.<p>It can be much worse though...exposing machine names, unnecessary complexity and parameters, all changing from year to year.<p>A server doesn't <i>have</i> to puke its implementation details everywhere.  I can't even count all the "enterprise" apps that make that mistake (e.g. a helpdesk system that gives me "serverNameThatWillChangeNextYear.domain.net/some/unnecessarily/convoluted/path.unnecessaryExtension?whatthehellisallthis&garbage1=a&garbage2=b&finallyRelevantBugNumber" instead of a stable URL like "company.net/bugs/bug123456".  And just try E-mailing a complex URL to somebody (it wraps, and time is spent to awkwardly correct it).<p>Honestly, it's as if most web developers don't understand how powerful URLs can be.  If you make URLs short and stable and use them to help look up stuff, they can be very nice.  Instead in the past I've seen people E-mailing 9-step instructions on <i>how to find something</i> because the damn URL is unreliable.