I like that it is easy for people in different states or even countries to register at once, which helps with keeping registrations up-to date! It's also great because of how many options there are when creating events such as choosing between two dates (start/end) - this makes things easier than if we had just one option available.
The only thing about groupnet that I dislike would be their customer service department; they can sometimes take too long to respond back. This has nothing really bad enough to say but rather something minor that could use some work. If anyone needs an event management system then definitely give them GroupNet a try! We have been able to easily keep our registrants updated by sending out emails via Eventbrite whenever someone registers so far.