Approximately nothing.
The average knowledge worker somewhat more, but lots of them are at the level of “I can consume a pivot table someone else set up”.
Sure, there are highly-productive, highly-skilled excel users that aren't traditional developers that can build great things, but they aren’t “your average person”.
https://news.ycombinator.com/item?id=26386419 (HN: Excel Never Dies)
https://news.ycombinator.com/item?id=20417967 (HN: I was wrong about spreadsheets)
https://mobile.twitter.com/amitranjan/status/113944938807223... (Excel is every #SAAS company's biggest competitor!)
We may not call them developers or programmers (or we might; I’ve been one of them as a fraction of my job at different times, both as a “fiscal analyst” by working title and as a “programmer analyst” by title), but effectively that's what they are, developers using (and possibly exclusively comfortable with) Excel as a platform.
Is it a coincidence that the same company that makes Excel is trying to… “democratize” and/or de-specialize programming?
I don’t really think so, but shrug.