If you have enabled "Allow Members to Reply" on your event then you will be able to keep track of who has responded within the Event Replies section contained within the list of all of your events.
You can see an overall view here of how many Yes/Maybe/No you have for each event.
A fuller view of each event can be found within the "Replies".
This is a handy way to keep track of who is coming to your event and who still needs to be chased for a response.