I wrote a small game a few weeks ago in flash 7. Now I've updated it to flash 8 to benefit from cacheAsBitmap, yet now key commands need to be rewritten. Check it out for yourself. Play the version 7 one first. Spacebar to shoot, 4 arrows to move the ship around. Also notice the performance increase with version 8.

Flash 7 version

Flash 8 version

This isn't the first time I've come across legacy issues. I have another application that uses XML and a few classes wouldn't work with the version 8 player. Had to debug and rewrite code to support 8, yet then wouldn't work under the flash 7 player. MM isn't doing to well with this new player. Beta or not, flash 8 is due out in 3 weeks, which means this beta version is final or near final.