What is the danger of sharing how many cups of coffee you drink?

I think the danger is more around how much alcohol you consume, especially if you do it around professional settings like user groups and hack-nights.

If your name can be tied to a HN account, and your account of drinking at developer events matches up with local stories of "that guy that gets drunk each month" then that's enough for sway some hiring managers towards another candidate.

It's an extreme example, sure, but most people do a few Google searches to see what comes up when a candidate comes in for an interview. In my experience, I've seen some...strange things come up on peoples Twitter accounts when I've done a quick check on them, and while I try to keep my decision to purely a skilled-based one, a lot of people will have their opinion on someone swayed by their actions online.