Can anyone give an example of a popular app where they've been consistently very confused by what's a clickable button/link?

I get that a chunky 3D button probably scores the highest in terms of advertising that it's clickable, but is e.g. the text "agree" and "disagree" in blue when all the text around it is black (from the article) so confusing you'd give it something like 1 out of 10 in comparison? Or is it more like 7 out of 10?

I've haven't found it a huge problem in the apps I use. HN has lots of links on the page that aren't underlined or even a different color to non-clickable text for example.

For what it's worth, WCAG for accessibility says buttons should have a visible border and hyperlinks should be visibly different to the body text (underlined, or a different color/brightness) so there are some standards and guidelines.