Good recommendations.

For the SAP Mentors I am hosting more than one webinars per week.
I don't have patience anymore for webinars without chat, it makes me antsy.

It is also surprising what a difference a web camera makes. The whole event is so much more engaging and we see the reaction to questions.

Under performance I would add that we can learn from theater, TV and radio: How do they stage performances: Intro, main finale, music, comic relief, …

How do they make their speakers feel comfortable and make them shine?

Have your main content down, but bring in some surprise and try some innovations.
I once did a little finger puppet show, makes it more fun for the organizers too.

Just my 2c, Mark.

We plan our webinars “backwards” – that is, we start with what we want to achieve out of the inititive, quantify it, and then lay in the integrated tactics and messaging to reach those goals.
I've found that there are three absoutely fundemental requirements for a sucessful webinar.

First, the sales staff needs to be part of the initiative from the very first meeting, as they have the primary responsibility for coverting attendence to sales. We have firm conversion goals and hold them accountable – whther our goal is increasing reach or making the cash regoister ring.

Second, there needs to be enough time to do the promotion for the event. Our least sucessful webinars are those we try to execute with less than ten days notice. Generally, we start our planning about four weeks out. That gives us enough time to try different messaging and media tactics.

And third, don't underestimate the intense effort involved in getting “fannies into seats”. Our partners, staff and sales team pound the phones (in adition to all of the varied direct response touches). We get nearly a doubling of attendees when we employ this tactic.