It's about the product. Users attend conferences to learn more about a vendor's software. So product needs to get a lot of air time. Yes, services matter too-but it's the product that people have taken time out of their busy schedules to learn about.
Have a motivational speaker who matters.
Demo software. Many attendees are expert users. Vendors need to demonstrate they, too, are experts with their own product. The best way to do this is to demo the product.
Subject expertise beats celebrity. Yes, user conferences are about inspiration, but a celebrity, soap opera star, or a talk show host is not something an enterprise software user can relate to their work and is definitely not why they spend 3-4 days and a few thousand dollars/euros to attend a conference.
Limit the philanthropy. It's great for vendors to give back to a purpose outside of the software. But it should not be 50 percent of a keynote.
Users want to network. Vendors should give users a chance to network. Not just informally, but in a planned way.
Party hard but responsibly.