Clearly the most important feature:
[Google found that] the page with 10 results took 0.4 seconds to generate. The page with 30 results took 0.9 seconds. Half a second delay caused a 20% drop in traffic. Half a second delay killed user satisfaction.
In A/B tests, [Amazon] tried delaying the page in increments of 100 milliseconds and found that even very small delays would result in substantial and costly drops in revenue.
Jeff Atwood’s piece is right on the money. Speed is incredibly important. None of the other features matter if the site is slow.
Over the past few years we made a few changes to Summer Sweat and the only one that increased our traffic, retention rate, and page views was the speed improvements that we made.