Sites that maintain their own shorteners for their own content are really the only acceptable exception, and even then it's still an extra thing that can break.
Several of my customers have been listed on the SBL because they ran unauthenticated URL shorteners, and of course, those shorteners were used to get around anti-spam URL blacklists.
Considering that no URL shortener I know of will actually let you change the underlying URL it points to, unless the hosting service decides to change what the underlying URL actually points to (tsk tsk), the shortener is pretty much a canonical pointer to that data, despite the fact that the hash doesn't often give much information about the underlying data.
Also: see http://www.301works.org
- rn.tl / lensrentals.com
- nbl.gs
- qr.cx
- tiny.cc
- urlcut.com
- url.ie
- va.mu
And to be honest, those 7 shorteners aren't exactly big fish in the URL shortener business.
http://www.archive.org/search.php?query=collection%3A301work...
Despite claiming otherwise, bit.ly hasn't uploaded a single short url to 301Works yet.