Question: Where should I stand in relation to my PowerPoint?

Ideally you, the speaker, should be center stage.  Unfortunately most presentation spaces are set up with the projection screen smack dab in the middle of the room.  This sets up your PowerPoint to be the center of attention not you.  This also keeps your audience from making as strong a connection with you as this photo demonstrates:

presentationscreen incorrect

If possible, I would encourage you to bring your own screen and projector so you can set up in such a way that you, the speaker, is center stage not the screen.  Set up the screen so that it will be to the left of the speaker if the speaker is facing the audience.  Why?  Because people read right to left.  When they are done looking at the screen, their eyes will automatically go to their right which is where the speaker should be standing.