A few months ago I registered to attend a seminar. A few days before the event I received a friendly e-mail reminding me to attend. Confirming attendance is a great idea. You should either call or e-mail attendees to remind them of the benefits of your event and make sure they have directions. Unfortunately, the person who sent out the e-mail "cc'ed" everyone. This meant our e-mail addresses were visible for all to see. We all fear spam and need to honor people's right to keep their address private.
If you do your confirmations by e-mail, be sure you "bc", blind copy, your attendees, most e-mail programs will allow you to do this. Your attendees will appreciate it.