When it comes to dating, this study written up at PhysOrg suggests more options equal less discernment. In other words, given an abundance of potential partners we tend to look at externals–height, weight, attractiveness. When we have fewer options, then we take the time to dig deeper–well, slightly deeper.
Putting on romance writer’s hat. Interesting that the setting in which hero and heroine meet can have this unconscious effect. Lots of ideas boiling, now.