I've seen it happen plenty of times and when travelling to a conference always check whether the corporate codes I can use will net me a better deal. The most significant price difference I've ever run into was a conference in Glasgow about 5 years ago - I booked my stay via cheapohotels.com (full cost must be prepaid, but some great deals, particularly on UK hotels) and paid around $150USD/night, whereas the conference rate was 189GBP/night!!!