I've already posted some of my comments in a previous thread "Hovercard hover placement issue", but got no answer, so I'm posting them again and also adding more problem reports. The idea behind this is good, the display is nice but it needs some modification to stop getting in the way of normal use of the encyclopedia.
First, hovercards shouldn't be displayed so quickly, to ensure that they are displayed because the reader wants them to, not juste because the mouse went over a link. I still have Navigation popups active (because it allows me to do more things, like fixing links to disambiguation pages) and I think that having a similar delay would be a lot better.
Other problems I have encountered are with clicking (I almost only use Ctrl+Click, so I don't know if the problems I saw happen also with simple Click) :
1) (already reported) Very often when I put my cursor over a link, I have to Ctrl+Click several times to have the link opening in an other tab in Chrome. Simply clicking where the mouse is doesn't work every time. Often, if I Ctrl+Click when the hovercard is poping up, the Ctrl+Click is lost, and the hovercard disappears and starts poping up again. Painful to use, I'm currently considering deactivating this feature.
2) (already reported) I've also seen an other situation, less frequent: sometimes, when the hovercard is completely displayed, Ctrl+Click doesn't work at all unless you move the cursor a bit. If you repeatedly do Ctrl+Click without moving the cursor, the only thing that happens is that text is selected in the hovercard: first word, then all text, then nothing, ...
3) (new report) I'm currently working on fixing ISBN errors, I'm using a page that lists all ISBN errors on frwiki . I often take one line, and Ctrl+Click on all the links in that line to open the articles each in a new tab. Sometimes, when I move to a new link, the hovercard from the previous link is still displayed, and sometimes, even if I have the impression of clicking on the new link, it's the previous link that gets opened one more time instead of the new link.