Which way is up?

Here's a newbie photo/video question: when I take a picture or a video on my iPhone 4s, it will display correctly on the iPhone, but when I copy/move it to my computer, most of the time it is upside down. Although rotating photos is easy in Windows, rotating videos requires more work (but can be done).

I typically hold the iPhone in "landscape" mode when taking photos/videos (i.e., long dimension parallel to the horizon), but should the bottom of the iPhone (where the start button is located) be to the right or left?