When you are using google docs forms so people can sign up to an event. Is it possible to make the form send out a confirmation email when someone registers?
It's possible but you'll need to do a little scripting
Sending an email after a form submission is such a common task that Google has a complete tutorial to show you how to do it.
Take a look at:
Just keep in mind that Google does put limits on the number of emails that can be sent. The limit depends on what type of account you have (ex. Education, Business, etc).
You can check your email use relative to the limit by calling:
Google Apps Scripting makes it easy to do complex tasks with some simple scripting. Just keep in mind that there are limits put in place to prevent abuse/spamming.