The planning of conferences is an art and science, as well as a cottage industry unto itself. If you've been to a well-planned conference you don't even notice. But if you attend a poorly thought-out event, you definitely feel it. Some Internet companies sponsor their own conferences under the guise of customer service, but they're primarily marketing and schmooze events. If you're such a company and you want to have your very own conference, you're in serious competition.
Location is everything.
This is a no-brainer, but it requires a mention anyway. The most popular cities for conferences are the ones that have other stuff to do at night, in order to encourage attendance. Pay attention to amenities. Not all hotels are created alike. Go for the hotels that cater to a business clientele.