Bill is of course correct on his response, once you find a good setting, most people do stick with it.
I personally keep mine at 50% and rarely change it, but I do sometimes lower it a little if I see an image is looking too processed.
Many people will keep theirs even lower, as low as 20-25%. Anything more than 50% is too much for most content... IMHO.
So sometimes you may find the need to dial it up or down based on particular content, it really all depends on your personal preferences.
Since the player offers 3 different "mode" settings, you could put in 3 different settings and easily switch between them if desired.
There is also a Darbee button right on the remote where you can change it on the fly.
And again you can just find a middle-of-the-road comfortable setting like maybe 35% and leave it there.
As far as having the player calibrated, there shouldn't be a need for that.
However the calibrator may possibly want to take advantage of some of the "enhancement" features in the video settings.
Again that may be a personal preference as to how you want your image to look, and should be discussed directly with your calibrator.
Having said all that, as far as how the Darbee affects your calibrated image... it shouldn't affect it adversely, as long as you don't dial it up too high.
The higher you dial it up, you will see some degradation on test patterns, but in real world viewing it's all relative as to how you think the image looks best to your own eyes
You can have Darbee on at a low to mid setting and still enjoy your calibrated settings.
My first experience with Darbee Visual Presence was when I started using the 103D, and I was skeptical at first.
However after having used it for some months now, I really like it and recommend anyone to get the BDP-103D.
Having the choice to choose between the -103 and the -103D, I would definitely get the -103D.
Oppo + Darbee = Awesomeness