Actually Web Conferencing has been around for quite a few years now, in different forms. It has really started to pick up steam recently with the high energy prices and "green" thinking of a lot of people.
The big market leaders are names like WebEx, GoToMeeting, Adobe, and Microsoft, but there are a lot of smaller companies that provide hosted services as well. I represent Great America Networks Conferencing and our way to standout from the 100 or so companies out there is the "concierge" type of service.
We have a Dedicated Conferencing Consultant that works hand in hand for training, support, practice sessions, and pretty much whatever it takes to make sure your conferences go how you want them to. Most companies give you a Help document and you are on your own, or possibly a small training session in a group might be offered.
It definitely pays to do your homework before using any company and look for referrals and the level of service they provide because honestly 90% of the software will do most of what anyone is looking for. It's the service that makes or breaks how you look during your presentations.
Anthony