Hardware

I haven't had much opportunity to play with the Galaxy S2 but from my experience with Droid devices (including my own) this is not built in. In otherwords it's not something that can be set in the "Settings" of the device.

It's also depends on the app. Most of the apps I've used that store data does give you the option as to where it wll be stored. I have used a few that just default to built in system memory too (but these tend to be just app settings and not actual data that will grow).

I also don't think there's an app that will just redirect apps to store to the SD card either...

That all said I have noticed that majority of the apps I've installed do tend to default to the SD card if it's available.

HTH...