>Expire the short URLs. If you do so, you break the implied permanence of URL's. Users (who you give the resulting short URL's to) would be very confused when

>Expire the short URLs. If you do so, you break the implied permanence of URL's. Users (who you give the resulting short URL's to) would be very confused when they get directed to a totally different site. Though... I admit that we often use URL shorteners as a temporary device, and do not actually need to keep them beyond a few minutes or hours. I suppose it would be better to use long/descriptive URL's for the more permanent links, but then we would not need this service.