Craigslist.<p>Take the 10+ billion web pages out there, zoom in on the top 100 by traffic, which one is <i>effectively</i> used by the maximum number of people for non-trivial tasks?<p>Craigslist is at or among the very top of the list. I don't count Google, which is meta—they are a "portal" of the web. I discount Facebook for the same reason, as well as being 99.999% used for trivial tasks(teenagers sharing stupid photos, etc).<p>Think of web users as a strictly economical <i>force</i>, and ask which web site has the most real-world impact? Craigslist is 99% about real-world money changing hands. Buyer, meet Seller. Google, Facebook, the Silicon Valley Bubble Chamber, and almost all the biggest web properties/brands on the web are <i>derivative</i> products. Their value is based on the value of something else, or the value of a collection of something else.<p>I often wish Craiglist would add a simple counter to their site displaying a total value of good exchanged, similar to what many new sites show. Even if only a fraction of commercial exchanges could be tracked through some half-hacked manner, I bet that dollar amount would be a very large and surprising number.<p>Craigslist loses all design awards. This is true. It is an eternal relic enshrining HTML web design circa 1999, it has a hideous, redundant UI, it mercilessly makes users do too much work to sift and sort through what's out there, and provides no tools to lessen at least some of the work. And there's no way to extend or scale it it beyond doing individual, in-person transactions. Yet Craigslist blithely meanders on its merry way in 2010 without needing to partner or integrate with any other major web properties, any "Tech Coast" corps, any telecoms, nor are they beholden to Wall St in any way.<p>Name one other site that defeats this same set of constraints?<p>As for how this relates to design proper, the best <i>designs</i> are those you don't even see, and which optimize some set of material constraints that you don't even know about.