It shouldn't, but you may find that there are apps that aren't entirely compatible with ICS and will need to be updated. As far as your documents and media files, they should stay the same. All effort has been expended to make this an in-place update, but going from Gingerbread to Ice Cream Sandwich is a major step and I'd highly recommend that once you update you perform a factory reset and reinstall everything just to clean up the OS. Make sure you back up ALL your important data before you do, or you could lose it.
I believe the update is 4.0.3