You forgot to touch on the privacy issue, if you have to go through a central point to get a translated URL they can track your IP (and account and possibly name if the same company does the service) and what sites you visit.
Same trap google came up with when they released their free DNS service.

...isn't it, that URL shorteners introduce the familiar trade-off between convenience and performance? It's quicker and easier for the user to type in, but adds a level of indirection to the process.

recognise shortened URLs and retrieve the long version before the user needs it.

However, this doesn't fix every disadvantage. I think for tinyurl in particular I have it pause on the tinyurl site to tell me where I'm about to go. It may be somewhere I don't want to be.