I have stuffed ~900 KML files from tracks.org.nz into a geo database and displayed them in a map.

Each map move event queries the db for the currently visible tracks, this allows me to display a large data set, that would not be able to all be rendered at once.

This is a proof of concept so apologies to Firefox users if its all a bit slow. 

I am trying to keep the number of points as low as possible by using postgis' simplify() on the line data when zoomed out and using bounding boxes when zoomed out even further. You'll notice line complexity increases as you zoom in.

Next step is displaying info bubble with all the track details when a track is clicked on.