Fingernails have always been this way, haven't they? I have heard that fingernail damage is even more likely to lead to fatal infections now, but that might just be because danger rooms are apparently more dangerous now. Haven't ever used one so I don't know really. In any case, I'm pretty sure this can be fixed by editing the raws too. Adding a healing rate to the nail tissue should be all that's needed. I know that works for making hooves heal anyway.
Anyway, the .40 line is still kind of wonky in some ways, yes. It's not cripplingly buggy anymore, and in fact has fixed a lot of really old and annoying bugs. The biggest complaints right now seem to focus on the morale system, which is pretty broken in both fort and adventure modes right now. Things run away from just about anything now, which can make stuff... difficult. A few features still aren't completed either, like handling of plants and harvesting of fruit from trees. No ETA on when that will be finished.
It's probably fine to play now, really. Save compatibility has been preserved for quite a few versions now so you probably don't have to worry about that at least. You'll probably still see the occasional hiccup, like stuff getting stuck in trees or almost unkillable zombies, but it's not too buggy to at least start familiarizing yourself with the changes.