cairo = teh win.
Stuffing thousands of data points into one SVG file and letting the browser/PNG renderer figure out how to smash 'em into a smaller graph (i.e. downsample) = teh win.
(As you probably figured, I'm on the year-end geekiness overdose. Talk to me and expect to be showered with irrelevant PostgreSQL, cairo and/or Python jargons that make absolutely no sense. XD)
P.S. Before you go hide and cower, Alex, yes, you are excepted. XDD