I am probably missing something, but I would like to follow a tag on MathOverflow, so that I get emails about new questions with this tag. How do I do this (I read MathOverflow help and Googled this question but couldn't find the answer; on the other hand, I can follow individual existing questions but this is not quite what I would like to do). Thanks!
There's a feature 'Filtered Questions' on stackexchange.com. Just go to https://stackexchange.com/filters/new and fill out the form:
That works for email; if you're more into RSS feeds, there is a link at the bottom of the right sidebar of the [tag page]: