There are a few reasons for this. In past years we have come into conflict with other groups using #CIL<year> including one year when our event took place concurrently with an S&M event in Cairo Egypt that happened to have the same CIL initials.
Also, a “tweet record” includes a date so it is pretty easy to figure out which Computers in Libraries conference a tweet is referring to when you see it.
And finally, there is no reason anymore to treat Twitter like a passing fad or only a website based service. People use a wide array of Twitter clients and by using a consistent tag — year after year — people who program saved searches into their Twitter clients will see the tweets about each years events as early as they wish to. This means they do not miss the Call for Speakers alerts or questions from the planners and organizers.
This year we will again be archiving conference tweets and making them available after the event ends. The only hashtag our archival system will be watching for is #CILDC. If you wish to ensure your tweets make it into the archive, please use that hashtag. If you use others it will not prevent archiving as long as that tag is somewhere in your tweet.