score:5
Yes. Three times. Accepted in all cases although visa was denied in the third case for a different reason. I believe online statements are the norm, unless in parts of Africa like my original country where it probably won't carry much weight.
My statements were not stamped by a bank. Indeed the first time I went to get them stamped at Bank of America. They refused because they said online statements are acceptable as is for official purposes.
Like I wrote that might not be the case if applying in some of the developing countries (e.g. Nigeria) already noted for high incidence of fraudulent documents. In my home country Ghana for example bank statements are not printed on normal A4 sheets so a statement printed from online on A4 sheets will be clearly physically different from one printed in a bank. I would not risk it. Better safe than sorry