Zander:"Why is the mezuzah tilted? Why is it diagonal and not horizontal or vertical?"
The answer (compliments of Wikipedia): "Ashkenazi Jews and Spanish and Portuguese Jews tilt the mezuzah so that the top slants toward the room into which the door opens. This is done to accommodate the variant opinions of the medieval Rabbis Rashi and Rabbeinu Tam as to whether it should be placed horizontally or vertically, and also to imply that God and the Torah (which the mezuzah symbolizes) are entering the room. Most Sephardim and other non-Ashkenazi Jews affix the mezuzah vertically." More info on how and where to affix a mezuzah can be found here.
What I said: "Time for bed!"P.S. I would be remiss if I did not mention that Brad did the research and put up the mezuzahs in our home.
P.P.S. The photo at the top is NOT of the mezuzah on Zander's doorpost.