I've only ever managed to get around 100,000, and that's with the help of the little power-ups that you can get. I really suck at the game for some reason. I'm convinced that it hates me and purposely loads bad games that have hardly any jewel matches. >.<
I had 404k once but that was mostly luck. I think I got about 100k of it at the end when all your leftover special ones explode.