We haven't done it this year, but have been to CP a Friday of Halloweekends many times over the past five or six seasons. It is a great night to go - although not every ride is running and the park is only from 6PM-11PM, all the haunted attractions are open, and the crowds can be very light. Most of our Friday visits the coasters were walk-ons all night (except for Millennium Force, which would have maybe a fifteen minute wait), and it's great going through the Fright Zone with so few people around.
Speaking of which - they've added a new Fright Zone for this year over by Wicked Twister, themed to "scary" clowns. We would love to get down there if we get a chance ...