I've been using the Mac version for a month or so now. My experience has been pretty pleasant: the slight hue shift serves both to decrease eye strain and to suggest that it's getting late (an unintended but useful consequence).

I personally am not sure that the ease on my eyes really comes from the hue shifting or simply from the reduced contrast, but either way I enjoy the effects of the program.

Easily the biggest problem I have is that the Mac version doesn't actually gradually shift hues and so when it makes its sudden change at around 7pm it literally hurts my eyes as they attempt to adjust.

I'm not sure if it alleviates eye strain, but using less blue light at night has a definite effect on your ability to get to sleep. (http://www.post-gazette.com/pg/08065/862394-51.stm)

It turns out that blue light even affects the circadian rhythms of blind people (http://www.scientificamerican.com/article.cfm?id=ask-the-bra...).

I just got the Linux version running. It definitely changed the screen color a lot. I guess we'll see whether it helps my eyes.