I really, really like DDG a lot so please don't take this in a negative way! In fact I've been promoting it extensively after the events this past week.
Results take a little while to show up, even using Google Chrome (with fast JS and such.) I wonder if the delay of results is the time to render or is it my weird queries hitting the backend SQL? Or the multiple requests and parsing JSON perhaps? On a somewhat weird query YSlow showed >1s for 3 of the 5 JS requests on the results page.
It feels a lot like YUI apps. Other people notice it. Also there's unease on running JS, but that's a more hardcore security base, not really that important in the big picture (I think.)
Have you considered using nginx modules for querying cache/sql and writing HTML directly?