Like Craigslist, people don't really have a choice with Facebook. You either use it, as ugly as it is, or don't.

I'm not sure what you mean. You mean they don't have a choice in the design? Because there were plenty of alternatives (MySpace). Facebook just provided a better experience.

Facebook's software might be better, their uptake was better, but that doesn't mean their site is more visually appealing. It just means it's more effective.

Function over form.