It's not the usual kind of charisma—I didn't feel a strong need to win his approval, relative to how much I do with other smart people. It's rather that he was extremely quick to understand my arguments and point out important aspects I hadn't considered, which makes it easier for me to consider that my argument might be flawed. So that's an aptitude, but it's one better correlated with good argument than the aptitude of charisma is.
I'm writing to recommend something awesome to anyone who's recently signed up for cryonics (and to the future self of anyone who's about to do so). Robin Hanson has a longstanding offer that anyone who's newly signed up for cryonics can have an hour's discussion with him on any topic, and I took him up on that last week.
I expected to have a fascinating and wide-ranging discussion on various facets of futurism. My expectations were exceeded. Even if you've been reading Overcoming Bias for a long time, talking with Robin is an order of magnitude more stimulating/persuasive/informative than reading OB or even watching him debate someone else, and I'm now reconsidering my thinking on a number of topics as a result.
So if you've recently signed up, email Robin; and if you're intending to sign up, let this be one more incentive to quit procrastinating!
Relevant links:
The LessWrong Wiki article on cryonics is a good place to start if you have a bunch of questions about the topic.
If you want to argue about whether signing up for cryonics is a good idea, two good and relatively recent threads on that subject are under the posts on A survey of anti-cryonics writing and More Cryonics Probability Estimates.
And if you are cryocrastinating (you've decided that you should sign up for cryonics, but you haven't yet), here's a LW thread about taking the first step.