URL shortening services are ubiquitous on Twitter and other cramped online spaces. They won’t all last, as tr.im has demonstrated, and their shutdowns could annihilate your linking history. If you own a domain, though, you can host your own service.
Even if you consider the links you’ve shortened for Facebook, Twitter, IMs and other services to be just of-the-moment, nothing-serious items that aren’t worth backing up, leaving a host of dead links lingering around the net isn’t good for anybody, or anybody’s searches. There’s not a lot you can do about your already-posted social network links, but anyone who’s got $10 for a domain name registration, and a creative short URL idea, can host, monitor, and control their shortened links.