With the announcementthat Twitter rival Pownce is shutting down on December 15, users of the microblogging service who want to save their posts had better do it soon. Following recent news of other high-profile on-line closures, like that of Sandy and Stikkit, the question is what other Web services will be shut down.

For the most people, losing their Pownce messages isn't going to be the end of the world, and they've still got time to export them. However, with Yahoo's continued financial troubles, Flickr might be next. The popular photo-sharing site was started in Vancouver, before it was bought out by Yahoo and moved to the U.S. If Yahoo runs into trouble, Flickr, which is reportedly a loss leader for the company, might disappear.

If Flickr went down, a lot of people, myself included, could find years' worth of their personal photographs vanishing into the ether.

The moral of the story? As much as we want to start storing all of our files and information on-line, "in the cloud" as the new phrase goes, it's still advisable to keep a backup of the really important stuff offline.