This shows me getting the highest possible medal on Bejeweled Blitz on Facebook applications by exploiting the timing window when the clock runs out (250k medal). To keep getting combos when the timer runs out, you need to select the next gem you want to swap before all the other gems are done falling. Once you have the desired gems selected repeatedly click the square that you want to swap. If you did it right, as soon as the gems on the screen all stop falling, your combo will go off and the gems will keep falling again, and if you're fast enough, you can keep clicking combos before the gems fall, keeping the timer from ending the game.
This is a very difficult thing to do.
If you can get over a X6 multiplier and then keep getting combos after the timer runs out, that is where the really insane scores come from.