By now, the World Heritage Organization has protected hundreds of sites ranging from beautiful natural islands to buildings in large cities to ancient ruins.

Is "by now" in the above equal to "so far" and "up to now?" Thanks.
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". I don't know how to explain it though...
So far and up to now sound more neutral to me, and it would sound like the process you've been considering is expected to continue in the future.
- We've had four storms so far. (More are likely to come)

On the other hand, by now seems to be used when some things are expected to happen, and with by now you set a point in time and consider those events from that point.
- They should be home by now. (They are expected to get home. I think now they are finally at home)

That's why I don't feel sure about "by now" in sentences like yours... You'd better wait for some native speakers. Emotion: smile
AngliholicIs "by now" in the above equal to "so far" and "up to now?"
Not exactly, no, but it is very similar.
by now suggests that the preceding text has already mentiioned the efforts of the WHO to protect these sites. It suggests that these efforts have been working well, so that by now (considering the on-going efforts), certain accomplishments have already been achieved.
George started off for Paris at 6 this morning on Flight 009. By now he has arrived in Paris.
(Considering the on-going progress of his plane toward Paris, we conclude that by now he has arrived.)
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To me by now implies that now is a deadline.
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