To Adrian's point, node IDs aren't useful to your casual web visitor. Therefore Drupal distros should default to include and have enabled pathauto and perhaps follow the WordPress model (the only model with which I'm familiar; if another system is better, I'd be interested in its structure as well).
I think WP doesn't use an intermediate table that contains (source URL, destination URL)-tuples. Instead, it directly translates the URL to a database query that looks up the post. Drupal: + Any URL can be aliased, not just those related to posts. + Any URL can have multiple aliases: 'team', 'about' and 'about-us' can point to the same page or content. (A bad idea as Google will penalize you for this.) - Performance penalty when URL aliases are enabled; up to 100+ queries/page. These queries are very fast though. + Very fast when URL aliases are disabled. WordPress: - Only some URLs can be aliased. - Limited to one alias per post. + Small performance penalty. - Not as fast as Drupal when URL aliases are disabled. -- Dries Buytaert :: http://www.buytaert.net/