The purpose of the event is to give both sides a deadline.
|Photo via SXC.hu|
On the one hand it lets customers know when they might expect the product to be available, and on the other it gives the entrepreneur a watershed.
If they're late delivering on their promised event, they going to have to back down. It's no biggie - but usually the customers will expect (and deserve) some kind of discount, or benefit from your failure to deliver on time.
Why the freebie?
The answer is simple : event based marketing works best when the customer has already paid to be a part of your empire. They've given you money; money that you needed to get the solution built, but money that they were hoping to save by using it.
If they can't use it, they deserve compensation. After all, they've been tempted on board with the promise of availability, and if you don't meet up with their expectations, they will be very disappointed.
So, plan your event so that there's a reasonable expectation on both sides that you'll make it, but be prepared to give generously if you experience a delay.
In the long run, your customers will be happier that way.