online event organization I believe, is a very useful tool for any company working in an event type industry. You can contact all the people who for some reason decided not to finish their registration email. I think you would see an increase in event attendance due to the sales marketer contacting the person and helping them over their hesitation.
From a personal view, if I was to book into a seminar and decided I didn't want to for some reason then I had someone call me in regards to booking in, I would be quite annoyed. Obviously if I stopped registering, I wouldn't want someone calling me trying to sell the event to me. Now that I know about this program I actually don't think I would register for anything online.
However, saying this, it is still good customer service, and if I was to receive an email stating that my email registration had not gone through, I would appreciate the notice.