Picking the right URL shortener for your links is obviously important, especially now that the fact that they might not be around for as long as you might like has dawned on people. Naturally you should roll your own, but failing that, it might be interesting to know that Bit.ly and Ow.ly are the most reliable ones. At least according to a reliability report from Pingdom. I must say, I was a bit surprised to see Ow.ly up on top, it has had some downtime in the past but have obviously got its act together. In fact, it was the only one with 100% uptime.
Be sure to read the whole thing. It is pretty interesting after all.