It's totally fine. It just means they will bump down to the next visual row, and space out responsively. Everything is floated left for that very purpose.
I do think the naming of .row creates some confusion, because a .row can span multiple "rows" of divs depending on your screensize and the # of divs you stack up.
No you can use like that; http://jsbin.com/gusawere/1, bootstrap 2.X had problems with that usage but 3.x dont.
It's totally fine. It just means they will bump down to the next visual row, and space out responsively. Everything is floated left for that very purpose.
I do think the naming of
.row
creates some confusion, because a.row
can span multiple "rows" of divs depending on your screensize and the # of divs you stack up.