500 hours. That is the cumulative number of hours that I have spent speaking in front of a group. That is three summers I taught courses with 40 lecture hours each; 8 quarters of graduate teaching assistantship; and 10 quarters of undergraduate group tutoring where I led lab lectures for an hour once a week before one-on-one tutoring. That is six conference presentations (and four practice talks), one in-house research presentation, an advancement proposal, and a commencement address. That is two guest lectures in a graduate class, and one in an all-girls' day school. That is at least one trite talk for general-education requirements (I lost count after one, because it matters so little).
I am not so nervous about public speaking anymore. It really does come with practice.