Very interesting question!
When I used to cube at lunch my senior year in high school and throughout my college years, if anyone had interest in the cube, then I would get a positive reaction from them at some point. If was is a lot on their minds, they were stressed, etc., then I would tend to only get glances. After exams or at the beginning of a term, before a break, etc., some of them would simply observe their surroundings more and notice.
However, I have gotten the most positive reactions from people of all ages: what they all have in common is that they have had an interest in the cube, are currently not too stressed with life at the moment in time, and are unaware that it's possible to solve the cube.
I found that if I solved it quickly (well, for me), less people in a crowd would notice unless I was directly in front of them. Acting like I'm struggling to solve the cube while I was solving the cube always worked like a charm.
In short, it only depends on the person, their current mood (including current stress), their interest in the cube, their level of awareness of the possibility of being able to solve it, and its difficulty.
EDIT:
Both genders reacted equally.