During October, WDW plays host to Symposium/ITxpo, sponsored by Gartner Group, one of the preeminent IT advisory services in the world. During January, WDW plays host to Lotusphere, sponsored by IBM. It's much smaller now than it had been five years ago, but still dominates the Epcot resorts area for a full week.
In both cases, there is no noticeable impact on park crowds. The impact to vacationers is simply reduced availability of hotel rooms in the Epcot resorts area, and the manner in which the convention layers a mantle of business-orientation and work-orientation on the public areas of the resorts -- mostly the Dolphin and Swan, but to a certain extent all five resorts are affected, and of course the walkways between all five resorts are affected. After our first experience as vacationers during Lotusphere (we were often participants in the past), we decided to try to stay in the Magic Kingdom area whenever we decided to vacation that same week.