I rag on Microsoft Sharepoint 2007 big time for creating a supposed "web" product that uses the file system semantics to generate the URL, thereby ensuring that any file system manipulation will break any link, but really, Google is no better.
The original Blogger allowed users to change blog titles without breaking links, but after Google bought the first revision made the links reflect the title -- so editing a title broke links. The newest Blogger revision  changed that, the url is based on the original title but it doesn't change on editing the title -- however changing the date will break the link.
Then there's Google's Picasa Web Albums. Try this experiment:
1. Create an album.Google's supposed to be composed of very bright math majors, so I'm guessing this isn't mere stupidity. I can only speculate on what's at work, but it's more than annoying. I believe, but have not confirmed, that SmugMug, for all its recent buginess, does at least get this right.
2. Share a link to the album.
3. Edit the album properties and change the name. Note there's nothing to warn you of the consequences of this seemingly benign act.
4. Every link to the album returns a page-not-found. No redirects.
 Google may have some warped beliefs about links and metadata, but I can now say, with great caution and trepidation and painful memories of a semi-botched data migration process, that the new Blogger is far better than the old one. Now that I've said that Google will certainly proceed to wipe out all my data ...