I think this chapter explained something which has struck me as strange for a long time:

If the killing curse can be stopped by love, how come only Harry ever survived? Its not like Lilly is the only person who ever loved anyone, nor the only person who would sacrifice themselves to save another.

Maybe the Potters possessed a new, experimental deathly hallow, one capable of stopping the killing curse (or, alternativly, an old one whoes purpose has been forgotton). It must have limits on its power, otherwise James and Lilly would have lived, and probably wouldn't have been tested thoroughly, otherwise Lilly wouldn't have seemed to panic so much (unless she was acting to stop Voldemort guessing).

This could be the stone which glowed, and it may or may not require a love/sacrafice to power it.