I've tried to figure out if there is some way to do this using the events module currently, but I don't think its currently possible. I have a need (and I would think it fairly common) for people signing up for events to be able to add some comment about their signup. nothing fancy, just a textbox which would let them say something about their signup. For example, I have a non-profit site, if we are doing an event that goes for multiple hours, but a volunteer wants to signup to work the event but can only stay for part of the time, right now they have to signup for the event, but then email the volunteer event coordinator and let them know they can only stay for this portion of time. Or if we have an event that needs people to take certain roles, they could enter which role(s) they could do. 

thks