Drop7 strategies - iPhone Screenshots

I am totally addicted to Drop7, new iPhone puzzle game.
A few links:

• iTunes store: [App]
• Touch Arcade review
• a flash version of the game that can be played for free (chainfactor)

The game looks very clean and professional, as my iPhone Screenshot shows (hold home-button and press sleep/wake-button, the screen will flash and the picture goes into the picture folder, credits) :
I won't go into the rules of the game, but I am interested in some strategical thoughts:

1. Obviously get rid of the low numbers first, noone wants to be stuck with 1s on top of everything else. So for instance drop 1s on grey numbers.
   (Especially in hardcore - get to the bottom of the screen in at least one column.)
   
2. Obviously crack grey numbers as quickly as possible.
   
3. Obviously use "chain-reactions", but how?
   a) build columns with the same number, they fall into place
   b) build "counting" rows, e.g. 12, 123 etc.
   

I have played the game for a while now and not come across many more strategies. But I have not been looking hard. Maybe I am missing something, maybe I will post some problems later on. Who knows more than I do?

High score: 215,023 (normal mode)