I like Awe.sm's approach. You own the domain and they do the URL shortening and analytics for you. Costs $99/year. I haven't used it, but it seems like a good way to make money in that area.
I thought about using this service, so we'd have control over our URLs...but the fact is, I don't trust awe.sm to stay in business forever any more than I trust bit.ly or tr.im. In the end, I decided to implement our own (haven't actually done it yet, but this is one of those cases where the people claiming to be able to replicate this feature in fifteen minutes aren't exaggerating).
Interestingly, I guess, this did make me stop and think about whether I wanted links to my company and products to disappear when these shortener services finally all come crashing down. Which is why I decided I needed to control it myself.
I'd already bought a pretty short name a couple of years ago with the intention of putting up a mobile version of our site on it.
I think that if they went out of business you can still have control of your link mappings. They claim that you can have portability, but I guess I don't know how extensive it is. It might just be click data that is portable. At the very least, if you own the domain you can point all the incoming links back to your home page. I see it as more of a cost vs. development time issue.
http://www.techcrunch.com/2009/05/04/its-awesm-create-a-powe...