Nowadays, every show attendee is vital, so it is particularly important to reduce the number of no-shows. Increasing the verification rate from 50% to 60% for a 6000-registered/3000-verified attendance show means 600 more bodies on the floor. Here are three tips (in addition to those on page 104 of the book):
Create an event at the last minute that addresses a very current concern of your attendees. For example, a free panel session on "Energy Efficient Widget Manufacturing" or "Profit from the Dot Com Meltdown". Then communicate this to all preregistrants.
Bribe exhibits-only preregistrants with a free pass to a seminar or other paid conference session. But you must communicate this preshow so it becomes a motivation to come. Either put the pass in the badge package that is mailed out or e-mail a downloadable version.
If you reward others (exhibitors, associations) for generating attendance, only pay for attendees who actually show up.