That was using 2 different ISPs and per-flow load balancing. Speed test.net servers can be configured to run in single and multi-threaded modes. It's not quite there upload wise but works fine downstream.
The router I use can load balance 4 PPPoE lines however it does not have the horsepower to run 4 x 76Mb at line rate.
There is some nice kit out there. PPPoE sadly mostly implemented in software, so 4 x PPPoE links running at 76Mbps and suddenly you need a full Intel Core series CPU, not often fitted to routers
James BT Infinity 2 19/09/2012 - Sold 42/6 - Getting 49/8.5 - Sync 53 / 9.5 Mbps @ 470m approx
14 years of broadband (ntl: cable to BT FTTC) - Router: Asus RT-N66U - Modem: Huawei HG612 speedtest