I read everything that comes through this form, and I answer most of it, usually within a week. The things I am most glad to receive:

• Corrections. A wrong number, a broken link, a claim that does not hold up, code that fails on your machine. Tell me the lesson and the step, and what you saw.
• Questions about a lesson. If something was unclear to you, it was probably unclear to others; I fix the lesson rather than just reply.
• Datasets that belong on the data page, and links there that have died.
• Teaching. If you are using these lessons in a course or a workshop, I would like to know, and I can usually help.

If you would rather not use a form, I am on Twitter at @thinquanaut, and the same handle reaches me at gmail. Please do not send patient data or anything confidential through either.