Like you said yourself, it's mostly about context in my eyes. If I'm watching a harem comedy, I'll accept pretty much any amount of fanservice. The genre is pretty much made for it, and if I didn't want fanservice, why would I be watching? My only problem is when it intrudes on a genre it doesn't mesh so well with, like a heart-warming family story, a serious drama, et cetera.
At any rate, I also kind of feel like "less is more" holds true for this kind of thing. Just one little mildly fanservicey scene with an otherwise classy female character can be really appealing, but by the end of Highschool of the Dead, for instance, I had pretty much grown cold and jaded and started mentally blocking out all the bouncing and jiggling.