People watching. We all do it. On a cruise everybody has a story, even if they don't post online about it. (Like you should in our message boards!) For my money, next to the sunsets and watching the water and ships, people are the most interesting thing to do many nights. On Oasis of the Seas these past two cruises, I've tucked myself in defilade with a Coconut Ranger Cookie or slice of pizza, a bit of ice tea and "people watch."
Formal nights are the best for this passive activity. Those nights above all others, you get to see folks as they'd like to see themselves. The formal outfits, old party dress', and those non-conformists who just slum in any old thing. Added to the mix are a legion of photographers, who seek to entice you to get your photo taken. You'll notice that more and more the public spaces become rigged with lines and rope fences to either guide people closer to photographers or protect choice locations from being invaded as they are used in pictures. In truth folks line-up for these photo-ops. With digital media, online sharing options and the lower cost of non-film based photos, the lines are able to offer a lot more for the money. People clearly respond as well.
To traditionalists lament the lack of wide adherence to a single dress standard it does underscore that folks are free to do as they wish onboard.