Lack of them is becoming a pet peeve of mine. To me it makes a story difficult to follow. I am not sure whether I am more sensitive to it or it is more prevalent in stories now being published. It is not just on the this site, as I've seen it in ePubs I purchased.
As always, there are the occasional typos in ANY book (i.e. missing or mismatched quotation marks). But the worst are new authors who simply don't 'get' how quotations work or simply don't give a F*ck. Those are the worst.
The ones with the older British quotations have never bothered me, as I recognize those easily and easily adapt as well.