Regarding your first point, it’s also worth noting that the multiplier goes up as the size of the audience. Based on my short-lived experience teaching a college class, you need at least 2 to 3 hours of prep work for each hour of class time. If you do it right, the boost to your reputation can be worth it, especially if you aspire to give more presentations.

I’m totally with you on the confidence issue, too. Knowing the subject well goes a long way to making a smoother presentation.

As for your last point, I really need to work on that for the presentation I’m giving at the end of the month.

I expect that I’ll be pillaging your blog for more good ideas!