When I view ~10 year old web sites and forums it's rare enough that external links work at all, with all these link shorteners it's going to be even worse.
I imagine in the not too distant future that link shorteners will no longer be used (for one of many reasons), if/when that day comes most link shortening sites will have no incentive to keep their service available, and it would be hugely tempting for them to modify existing links to display relevant targeted ads, instead of the destination pages. Hell I wouldn't be surprised if many of them exist purely with that intention.
I also hate shorteners. But marketers love them, because they give them statistics. So they will be still in use, alas. The point is to improve them a bit.
URLs should be shortened and expanded in the browser, according to an RFC scheme. No third party and they live as long as the RFC's implementation does.
I would prefer to hover over a link and have my browser tell me where the link goes, not relying on some third party.
Why? Twitters URL shortener is also used to prevent spamming. In addition Twitter tries to detect malicious content and warn the user about it. They have reasons why they lengthen shortened links...
Reliance on a third party.