Micro-blogging service Tumblr has been seriously beating up on its smaller competitor Posterous. Pascal-Emmanuel Gobry postulates on the Business Insider (part of Silicon Alley Insider) that the biggest reason has little to do with features or fundamental support, but rather is due to Tumblr's superior design.
"Meanwhile Posterous is typical of the Silicon Valley engineering mindset where everything is measured, ranked, weighted. It’s like Google. And having terrible design like Google is great if you have a technology edge. But if you’re in a market where what matters is design edge, that’s not enough. There needs to be great design, by which I don’t mean looks (though they’re important), but how it works for the end user."
Gobry also makes the point that "design focus" is more typical of New York-based companies than Silicon Valley-based companies, but I'll leave that argument to others. For me, the more important point he makes is that, "for consumer web apps today, design matters more than technology."