Server-side crossfilter, eliminating the need to download the full dataset to the browser (<a href="https://github.com/ZJONSSON/crossfilter" rel="nofollow">https://github.com/ZJONSSON/crossfilter</a>).<p>Maps from LMI.is, which just released it's geographic data free of charge (<a href="http://www.lmi.is/stafraen-kort-og-landupplysingar-lmi-gerd-gjaldfrjals/" rel="nofollow">http://www.lmi.is/stafraen-kort-og-landupplysingar-lmi-gerd-...</a>)
This is neat. Digging through the source to see how you're doing marker loading and clustering. One of the things I've been chewing on recently is making maps with many (>1000) markers behave smoothly. Seems like you've nailed it.