Interesting question. I am interested too, since I am still afraid of by now's in sentences like the one you wrote, LOL. The point is I am not even sure it's ok, but if it is, I wouldn't say it's exactly the same as "so far" or "up to now".
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AngliholicIs "by now" in the above equal to "so far" and "up to now?"Not exactly, no, but it is very similar.