I don't understand the level of complaints on HN about that sign up overlay. Are they testing multiple nag screens and I got lucky and always get the minimally intrusive one, and the rest of you getting the terrible ones?

Yes, it is slightly annoying, but it is extremely easy to dismiss. Unlike the nag screens at many sites you don't have to find and click an 'x' in some weird location. It goes away if you click anywhere on the page outside the nag screen.

It also goes away if you hit ESC on the keyboard. (I don't know if other keys also dismiss it too. I've only tried ESC).

Furthermore, also unlike many other sites, it comes up right away rather than waiting for you to get into the article and then interrupting you. So it is click on a Medium link, get shown the nag screen immediately if it is going to be shown at all, and then hit ESC or click somewhere and it goes away.