Just though id share that am experencing a bug found whilst trying to install apps from the Market/Google Play with SGS2 on Miui v4. Certain apps when you try to install them fail and display the message Error Couldn't install on USB Storage or SD Card and so far I have had this on Where's my Water? & Burn the City. I believe this is actually an issue that was apparent with one of the ICS beta's leaking for the SGS2 so guessing thats the base that has been used for Miui v4. Nice easy soloution though and that is to unmount the SD card whilst installing the app, either through settings or just connect USB and mount and app installs fine and can unount afterwards. Just thought id share for anyone who didnt already know this.