Yarn Acquisition Syndrome (as defined by the crochetlist@egroups.com dictionary): The habit of collecting yarn.
Symptoms of this syndrome may include one or more of the following: the inability to avoid the craft sections of stores such as WalMart and Zellers; the tendency of one's car to automatically steer towards yarn and craft stores frequented by the sufferer; and an urgent need to find more and more storage space for the yarn purchased.
I freely admit to having this disease, though at this point it seems to be merely a mild case. Of course, considering the amount of space the yarn is taking up in my tiny apartment, perhaps it's not so mild after all...